Most islands belong entirely to a single country. A fascinating few, however, are divided between two sovereign states. These islands shared by two countries can have international borders running across their land, creating some of the world’s most unusual political boundaries.

The reasons behind these divisions vary. Some resulted from treaties and colonial-era boundaries, while others emerged from wars, political agreements, or long histories of territorial change. In some places, the border is obvious. In others, you can cross from one country to another without seeing much more than a sign or a line on a map.

This article focuses specifically on islands divided between exactly two countries. Islands shared by three or more countries are excluded from the main list, even when they are fascinating examples of international geography.

From large islands such as New Guinea and Hispaniola to tiny border islands with remarkably complicated histories, these divided islands show how political boundaries can transform a single piece of land into two distinct territories.

These islands can occur in seas, oceans, or rivers, depending on where the international boundary crosses the landmass.

What Does It Mean When an Island Is Shared by Two Countries?

An island shared by two countries is one physical landmass divided between two sovereign states. A political border crosses the island, giving each country control over its own territory.

The island itself remains a single geographic island. The international boundary simply separates the territories administered by the two countries.

These borders can exist for many historical reasons. Treaties, wars, colonial boundaries, and later political agreements have all shaped the borders found on divided islands.

Importantly, “shared” does not necessarily mean joint ownership. In most cases, each country has sovereignty over a defined part of the island rather than both countries jointly governing the entire island.

The border can be obvious or surprisingly difficult to notice. Some divided islands have formal border crossings and checkpoints, while others have little visible indication that you have entered another country.

For this article, we focus specifically on islands divided between exactly two sovereign countries. Islands divided among three or more countries are not included in the main list.

Islands Shared by Two Countries at a Glance

#	Island	Countries	Region / Key Feature
1	Hispaniola	Haiti & Dominican Republic	Caribbean — one of the world’s largest divided islands
2	Saint Martin	France & Netherlands	Caribbean — French and Dutch territories
3	New Guinea	Indonesia & Papua New Guinea	Oceania — one of the world’s largest divided islands
4	Timor	Indonesia & Timor-Leste	Southeast Asia — international border divides the island
5	Ireland	Ireland & United Kingdom	Europe — two political jurisdictions
6	Tierra del Fuego	Argentina & Chile	South America — main island divided between two countries
7	Sebatik Island	Indonesia & Malaysia	Southeast Asia — border crosses the island
8	Märket	Finland & Sweden	Baltic Sea — unusually shaped boundary
9	Usedom (Uznam)	Germany & Poland	Baltic Sea — popular holiday island divided by a border

1. Hispaniola — Haiti and the Dominican Republic

Hispaniola is one of the clearest examples of an island shared by two countries. Haiti occupies roughly the western third of the island, while the Dominican Republic occupies most of the eastern portion. Hispaniola is the second-largest island in the West Indies, after Cuba.

Where Is Hispaniola?

Hispaniola lies in the Caribbean, between Cuba to the west and Puerto Rico to the east. The island forms part of the Greater Antilles and has coastlines along both the Atlantic Ocean and the Caribbean Sea.

The island contains the entire territories of two independent countries: Haiti and the Dominican Republic. The Dominican Republic covers about two-thirds of Hispaniola, while Haiti occupies approximately the western third.

How Is Hispaniola Divided?

An international land border separates Haiti from the Dominican Republic across Hispaniola. The division has deep historical roots in the colonial period, when the western and eastern parts of the island came under French and Spanish control.

The Treaty of Ryswick in 1697 formally transferred the western portion of the island to France. Spain and France later defined their colonial boundary more precisely through the Treaty of Aranjuez in 1777. Parts of the present-day border still follow this historical boundary, although later agreements modified sections of it.

Today, the two countries remain politically separate despite occupying the same geographic island.

What Separates Haiti and the Dominican Republic?

The Haiti–Dominican Republic border runs for roughly 380–388 kilometers across the island. Its course is marked by a combination of natural features and surveyed boundary markers.

The border extends from the northern coast near the mouth of the Dajabón or Masacre River to the southern coast near the Pedernales River. The Dominican Republic’s border authority notes that 311 numbered concrete markers were established along the frontier.

The landscape changes considerably along the boundary, passing through mountains, valleys, rivers, agricultural areas, and populated communities.

Can You Cross Between the Two Countries?

Yes. Haiti and the Dominican Republic have official land border crossings, allowing people and vehicles to travel between the two countries.

However, crossing the border is an international immigration procedure, not simply moving from one part of the island to another. Travelers must use an official crossing and comply with the applicable immigration requirements. Current U.S. travel guidance identifies four official crossing points: Malpasse–Jimaní, Ouanaminthe–Dajabón, Anse-à-Pitres–Pedernales, and Belladère–Comendador.

This makes Hispaniola a fascinating example of how one geographic island can contain two completely separate national territories.

2. Saint Martin — France and the Netherlands

Saint Martin is one of the world’s most unusual divided islands. A single Caribbean island is split between the French Republic and the Kingdom of the Netherlands, with the French territory occupying the northern part and Sint Maarten occupying the southern part.

Where Is Saint Martin?

Saint Martin lies in the northeastern Caribbean, in the Lesser Antilles. The island is shared between Saint-Martin, an overseas collectivity of France, and Sint Maarten, one of the four constituent countries within the Kingdom of the Netherlands.

Although the names look similar, they refer to different parts of the same island. The French side is generally called Saint-Martin, while the Dutch side is Sint Maarten.

How Is Saint Martin Divided?

The division dates back centuries. France and the Netherlands established the basic land boundary through the Treaty of Concordia, signed on March 23, 1648. The agreement followed periods of rivalry between European colonial powers and established the division between the French and Dutch sides.

The boundary has changed in detail over the centuries, but the basic French-Dutch division has endured. A newer agreement signed in 2023 further addressed the delimitation of the boundary between the French Republic and the Kingdom of the Netherlands.

Today, the northern side is French Saint-Martin, while the southern side is Sint Maarten, an autonomous country within the Kingdom of the Netherlands.

What Separates France and the Netherlands on the Island?

The international boundary runs across the island, separating the French and Dutch territories. However, it does not resemble the heavily controlled borders found between many countries.

A border monument near the traditional boundary marks the division, but much of the border is visually unobtrusive. This makes Saint Martin particularly unusual: visitors can move from one side of the island to the other without encountering a conventional immigration checkpoint.

The distinction is nevertheless real. The two sides have different governments, legal systems, currencies, and political relationships with France and the Kingdom of the Netherlands.

Can You Cross Between Saint Martin and Sint Maarten?

Yes. The land border between the French and Dutch sides is generally open, with no routine border controls for people traveling between the two sides. Visitors can therefore explore both parts of the island during the same trip.

That unusual arrangement is one of Saint Martin’s biggest geographical curiosities. You can cross an international boundary on foot or by road and barely notice that you have entered another jurisdiction.

For travelers, however, crossing the open border does not erase the separate immigration requirements of France and Sint Maarten. Entry requirements can depend on nationality and the purpose of travel, so visitors should check the current rules before their trip.

Saint Martin demonstrates that an international border does not always create a dramatic physical separation. The island remains geographically unified, while two different political jurisdictions coexist within its relatively small area.

It is therefore a particularly clear example of what it means for one island to be shared by two countries.

3. New Guinea — Indonesia and Papua New Guinea

New Guinea is one of the world’s largest islands and one of its most remarkable divided islands. Its western half is part of Indonesia, while the eastern half forms the mainland of Papua New Guinea.

Unlike Saint Martin, where the international border crosses a relatively small Caribbean island, New Guinea is enormous. Its division separates two countries across a landscape of mountains, forests, rivers, and remote communities.

Where Is New Guinea?

New Guinea lies north of Australia in the southwestern Pacific region. It is the world’s second-largest island, after Greenland, and covers roughly 785,000 square kilometres.

The island stretches for more than 2,400 kilometres from west to east. Its central highlands include some of the most rugged terrain in the region.

The western portion is administered by Indonesia and includes the Indonesian provinces of Papua and Southwest Papua. The eastern portion is occupied by Papua New Guinea, an independent country since 1975.

How Is New Guinea Divided?

An international land boundary divides New Guinea roughly along its central-western region. Indonesia controls the western portion, while Papua New Guinea controls the eastern portion.

The boundary has its origins in the colonial history of the island. European powers divided their spheres of control during the nineteenth and early twentieth centuries, with the Netherlands controlling the western portion and Australia administering the eastern portion before Papua New Guinea became independent.

The modern Indonesia–Papua New Guinea border was established following the transfer of the former Dutch territory of western New Guinea to Indonesia.

What Separates Indonesia and Papua New Guinea?

The international border runs through some of the island’s most remote terrain. It extends for approximately 820 kilometres, from the northern coast to the southern coast.

Much of the boundary passes through mountainous and heavily forested areas. The rugged landscape makes many parts of the border difficult to access.

The border also separates communities with long-standing cultural and family connections. In some areas, traditional communities have existed on both sides of the modern international boundary.

Can You Cross Between Indonesia and Papua New Guinea?

Yes, but crossing is considerably more restricted than moving between the French and Dutch sides of Saint Martin.

There are official border crossings between Indonesia and Papua New Guinea, including the major crossing near Jayapura, Indonesia, and Vanimo, Papua New Guinea. Travelers must comply with the immigration and border requirements of both countries.

The remote nature of much of the frontier means that it is not possible to cross freely wherever the boundary happens to pass.

New Guinea stands out because of its sheer size. It is not simply a small island split by a political boundary. An enormous and geographically diverse island is divided between two sovereign countries.

It also demonstrates how modern political borders can divide regions whose people, cultures, and ecosystems existed long before the international boundary was established.

4. Timor — Indonesia and Timor-Leste

Timor is another major example of an island divided between two countries. Indonesia controls the western part of the island, while Timor-Leste occupies the eastern part.

The island is particularly interesting because Timor-Leste also includes Oecusse, a small enclave surrounded by Indonesian territory on the western side of Timor. This creates an unusual political map on an already divided island.

Where Is Timor?

Timor is located in the eastern Lesser Sunda Islands of Southeast Asia, north of Australia. It is the largest island in the eastern part of the Lesser Sunda chain.

The island is divided between Indonesia and Timor-Leste. Indonesian territory occupies the western portion, while Timor-Leste controls most of the eastern portion.

Timor-Leste also includes the Oecusse region, which lies separately from the country’s main territory and is surrounded by Indonesia.

How Is Timor Divided?

The division of Timor has deep colonial roots. Portugal controlled the eastern part of the island, while the Netherlands established control over much of the west.

A series of agreements eventually established the colonial boundary between Portuguese Timor and Dutch Timor. That historical division later became the basis for the international border between Timor-Leste and Indonesia.

Timor-Leste became an independent country in 2002, following a period of Indonesian occupation and a United Nations-administered transition.

What Separates Indonesia and Timor-Leste?

An international land border separates Indonesian West Timor from Timor-Leste. The boundary stretches across the island’s mountainous interior and continues around the Oecusse enclave.

Unlike some divided islands where the border is barely noticeable, the Timor border is a significant international boundary with official crossing points and immigration controls.

The landscape along the border includes mountains, dry forests, agricultural areas, and rural communities.

Can You Cross Between Indonesia and Timor-Leste?

Yes. There are official land border crossings between Indonesia and Timor-Leste.

The best-known crossing connects Mota’ain in Timor-Leste with Wini in Indonesia near the northern coast. Other official crossings serve different parts of the frontier, including access to the Oecusse region.

Travelers crossing between the two countries must pass through immigration and customs controls and meet the current entry requirements of both countries.

Timor is unusual because its political division is more complicated than a simple east-versus-west split.

The island contains two countries, but Timor-Leste’s Oecusse enclave sits inside Indonesian territory. As a result, the political map includes an international border separating the main territories and another boundary surrounding an isolated part of Timor-Leste.

Timor therefore provides a fascinating example of how colonial history can shape modern borders—and how a single island can contain an unexpectedly complex political geography.

5. Ireland — Ireland and the United Kingdom

The island of Ireland is one of the world’s best-known examples of an island divided between two political jurisdictions. The Republic of Ireland occupies most of the island, while Northern Ireland occupies the northeastern part and remains part of the United Kingdom.

Unlike some divided islands, Ireland does not have two independent countries occupying separate halves. Instead, one sovereign country—the Republic of Ireland—shares the island with a constituent part of another sovereign state, the United Kingdom.

Where Is Ireland?

Ireland lies in the North Atlantic, west of Great Britain. It is the third-largest island in Europe and is separated from Great Britain by the Irish Sea and the North Channel.

The island contains two political jurisdictions: the Republic of Ireland, an independent sovereign state, and Northern Ireland, which is part of the United Kingdom.

How Is Ireland Divided?

The political division of Ireland developed from centuries of English and British rule and a long history of political and religious conflict.

The Government of Ireland Act 1920 established separate administrations for Northern Ireland and Southern Ireland. Following the Irish War of Independence and the Anglo-Irish Treaty of 1921, most of Ireland became the Irish Free State, which later became the Republic of Ireland.

Northern Ireland remained within the United Kingdom.

The present international boundary therefore separates the Republic of Ireland from Northern Ireland, although its character has changed considerably over time.

What Separates Ireland and the United Kingdom?

The border between the Republic of Ireland and Northern Ireland runs for approximately 500 kilometres across the island.

Unlike many international borders, it is generally unobtrusive. Roads cross between the two jurisdictions without the traditional checkpoints and barriers commonly associated with international frontiers.

The border follows a mixture of roads, waterways, fields, and other surveyed boundaries. In many rural areas, travelers may cross it without immediately realizing they have entered another jurisdiction.

Can You Cross Between Ireland and the United Kingdom?

Yes. People can travel between the Republic of Ireland and Northern Ireland by road, rail, and other transport routes.

There are generally no routine immigration controls at the land border between the Republic of Ireland and Northern Ireland. This is closely connected to the Common Travel Area, which allows British and Irish citizens to move freely between the two countries subject to its rules.

However, the absence of visible border controls does not mean the jurisdictions are politically identical. The Republic of Ireland and the United Kingdom remain separate sovereign states, and Northern Ireland remains part of the UK.

6. Tierra del Fuego — Argentina and Chile

Tierra del Fuego is an archipelago at the southern tip of South America, divided between Argentina and Chile. However, the political division applies to the archipelago as a whole in a more complex way. The main island, Isla Grande de Tierra del Fuego, is divided between the two countries, making it a notable example of an island crossed by an international border.

Argentina controls the eastern portion of the main island, while Chile controls the western portion and several other islands in the archipelago.

Where Is Tierra del Fuego?

Tierra del Fuego lies at the southern end of South America, separated from mainland South America by the Strait of Magellan.

The archipelago contains numerous islands, with Isla Grande de Tierra del Fuego being by far the largest. It is also the world’s 30th-largest island.

The southern location gives Tierra del Fuego a dramatic landscape of mountains, glaciers, forests, lakes, and windswept plains.

How Is the Main Island Divided?

The Isla Grande de Tierra del Fuego is divided between Argentina and Chile.

Argentina controls the eastern part, including the Argentine province of Tierra del Fuego, Antártida e Islas del Atlántico Sur. Chile controls the western portion, which forms part of the Magallanes and Chilean Antarctica Region.

The modern boundary is largely the result of the Boundary Treaty of 1881 between Argentina and Chile. The agreement established a boundary through Tierra del Fuego and also addressed territorial arrangements in the surrounding region.

What Separates Argentina and Chile?

The international boundary runs roughly from the Strait of Magellan toward the southern part of the island.

The eastern Argentine section includes Ushuaia, one of the world’s southernmost cities. The Chilean side includes rugged mountains, forests, fjords, and extensive protected landscapes.

Unlike a simple straight line across a flat island, the boundary reflects historical agreements and the island’s geography.

Can You Cross Between Argentina and Chile?

Yes. There are official border crossings between Argentina and Chile on and around Tierra del Fuego.

One of the most important routes connects the Argentine and Chilean portions of the island through the Paso Fronterizo San Sebastián. Travelers can cross by road, but they must complete the required immigration and customs procedures.

An important practical detail is that the main road connection also involves crossing the Strait of Magellan by ferry when traveling between the Chilean mainland and Tierra del Fuego.

7. Sebatik Island — Indonesia and Malaysia

Sebatik Island is a small island divided between Indonesia and Malaysia. The international border runs across the island, with Malaysia controlling the northern portion and Indonesia controlling the southern portion.

Unlike famous divided islands such as Hispaniola, Sebatik is relatively little known outside Southeast Asia. Yet its unusual border makes it one of the clearest examples of how an international boundary can divide a single island.

Where Is Sebatik Island?

Sebatik Island lies off the northeastern coast of Borneo, in the Celebes Sea. It sits directly along the maritime boundary between Indonesia and Malaysia.

The island is divided between Sabah, a Malaysian state, and Indonesia’s North Kalimantan province.

Its location makes Sebatik particularly interesting because the island itself is split by the international border, while the much larger island of Borneo is divided among three countries: Indonesia, Malaysia, and Brunei.

How Is Sebatik Island Divided?

The international boundary runs roughly across the island from west to east. Malaysia controls the northern part, while Indonesia controls the southern part.

The border is largely a legacy of colonial-era territorial arrangements between British-controlled North Borneo and the Dutch East Indies. When Malaysia and Indonesia later became independent states, the historical boundary became an international border.

The division is therefore not based on any natural feature that physically separates the island. It is a political boundary imposed across one continuous landmass.

What Separates Malaysia and Indonesia on Sebatik Island?

A surveyed international boundary separates the Malaysian and Indonesian territories.

In some parts of the island, the boundary is marked by border monuments and boundary markers. In other areas, the tropical landscape makes the division much less obvious.

The border also passes through communities whose cultural and family connections existed long before the modern international boundary was established.

This creates an unusual situation where people living only a short distance apart can belong to different countries.

Can You Cross Between Malaysia and Indonesia on Sebatik Island?

Yes, but crossing the international border requires using authorized routes and complying with immigration regulations.

The island has official border facilities, including the Tawau–Nunukan border connection through the surrounding maritime area. Local residents also have long-standing cross-border connections, although movement is subject to the rules of the two countries.

Visitors should not assume that the border can be crossed freely simply because it may appear unobtrusive in some areas.

Sebatik is fascinating because the international border cuts across an otherwise continuous tropical island. There is no mountain range or wide river separating the two countries.

It also offers an unusual contrast with Borneo. Sebatik is divided between two countries, while Borneo itself is divided among three.

That makes Sebatik a particularly useful example when understanding the difference between an island shared by two countries and an island divided among several nations.

8. Märket — Finland and Sweden

Märket is a tiny rocky islet divided between Finland and Sweden. It lies in the Baltic Sea, within the Åland archipelago, and is famous for having one of the world’s most unusual international borders.

The islet is only about 0.03 square kilometres in area, yet an international boundary crosses it. Its border was deliberately shaped into an unusual zigzag to keep the historic lighthouse on the Swedish side.

Where Is Märket?

Märket lies in the Baltic Sea, between mainland Sweden and the Finnish-controlled Åland Islands.

It is part of the Åland archipelago, an autonomous region of Finland. The islet itself sits close to the boundary between Finnish and Swedish waters.

Despite its tiny size, Märket has attracted considerable attention from geographers and travelers because of its unusual political geography.

How Is Märket Divided?

The islet is divided between Finland and Sweden by an international boundary.

The present arrangement dates back to the nineteenth century. When the border between the Russian Grand Duchy of Finland and Sweden was established, the boundary had to pass around the lighthouse that had been constructed on the islet.

The result was an unusual boundary that does not simply run straight across Märket.

Instead, the border makes a distinctive zigzag shape, allowing the lighthouse to remain on the Swedish side while most of the islet belongs to Finland.

What Separates Finland and Sweden on Märket?

There is no large natural feature separating the two sides. The boundary is an artificial political line surveyed across the rocky islet.

Unlike a conventional international border with a fence or checkpoint, Märket has no permanent border infrastructure for travelers. The boundary is primarily significant because of its legal and geographical position.

The unusual shape is especially striking when viewed on a detailed map.

Can You Visit Märket?

Märket is extremely remote and exposed to the Baltic Sea. There is no regular tourist infrastructure on the islet, and reaching it requires suitable transport and favorable weather conditions.

The historic lighthouse is no longer an active navigational station and is not a conventional tourist attraction with regular visitor facilities.

Visitors should therefore treat Märket as a special-interest geographical destination, rather than an ordinary island vacation spot.

9. Usedom (Uznam) — Germany and Poland

Usedom, known as Uznam in Polish, is a Baltic Sea island divided between Germany and Poland. Most of the island lies in Germany, while its eastern section belongs to Poland.

Unlike many divided islands separated by dramatic geographical features, the border on Usedom runs through a largely low-lying landscape. In the town of Świnoujście, the international boundary is especially interesting because the urban area itself extends across the island.

Where Is Usedom?

Usedom lies in the Baltic Sea, off the coast of northeastern Germany and northwestern Poland. It is part of the southern Baltic coastline and is connected to the mainland by bridges, roads, railways, and other transport links.

The island covers roughly 445 square kilometres, although the exact figure varies depending on how its surrounding waters and smaller connected areas are measured.

Germany controls the western and larger portion of Usedom. Poland controls the eastern portion, including the city of Świnoujście (Swinemünde).

How Is Usedom Divided?

The division of Usedom dates from the changing political boundaries of Central Europe after the Second World War.

Before 1945, the entire island was part of Germany. After the war, the new German-Polish border was established farther west, placing the eastern part of Usedom within Poland.

The border follows the Oder–Neisse boundary system, which became the basis of the modern German-Polish frontier.

As a result, one geographic island is now divided between two sovereign countries.

What Separates Germany and Poland on Usedom?

The international border crosses the southern part of the island and separates German territory from the Polish section around Świnoujście.

For many years, the border was a much more significant physical barrier. Today, however, the situation is very different.

Germany and Poland are both members of the European Union and the Schengen Area, so there are generally no routine passport controls at the land border between the two countries.

In some locations, the boundary can feel almost invisible to visitors.

Can You Cross Between Germany and Poland on Usedom?

Yes. Visitors can travel between the German and Polish parts of Usedom by road, bicycle, or on foot.

The border became considerably easier to cross after Poland joined the Schengen Area in 2007. Today, travelers can move between the two sides without the traditional border checkpoints normally associated with an international frontier.

Usedom is unusual because the international border cuts through a popular European holiday island rather than an isolated or remote landscape.

The island’s beaches, resorts, cycling routes, and coastal communities extend across both sides of the border. Visitors can therefore experience two countries during the same island trip.

Its history also shows how political borders can change dramatically while the underlying geography remains unchanged. Usedom is still one island; only the political boundary across it has changed.

A Special Case: Pheasant Island — France and Spain

Pheasant Island is one of the strangest examples of an island associated with two countries. Located in the Bidasoa River between France and Spain, the tiny island has a unique shared-sovereignty arrangement rather than a conventional international border dividing it into two permanent territories.

France and Spain jointly hold sovereignty over the island, but neither country administers it permanently. Instead, control alternates between the two countries on a fixed schedule.

Where Is Pheasant Island?

Pheasant Island lies in the Bidasoa River, close to the border between France and Spain. The river itself forms part of the international boundary between the two countries.

The island is extremely small, measuring only about 200 metres long and 40 metres wide. It is located between the French town of Hendaye and the Spanish town of Irun.

Despite its tiny size, Pheasant Island has an extraordinary diplomatic history.

How Is Pheasant Island Shared by France and Spain?

Pheasant Island is not divided into a French half and a Spanish half. Instead, it is a condominium, meaning that France and Spain share sovereignty over the same territory.

The arrangement dates back to the Treaty of the Pyrenees, signed in 1659. The treaty was negotiated on the island and helped end a long conflict between France and Spain.

Rather than assigning the island permanently to one country, the agreement established a system under which sovereignty would be shared.

Who Controls Pheasant Island?

Administration of the island alternates between France and Spain.

France administers Pheasant Island for part of the year, while Spain administers it for the remainder. The responsibility changes every six months.

This makes Pheasant Island one of the world’s most unusual examples of shared territorial sovereignty.

The arrangement is sometimes described as a condominium, rather than a divided island, because both countries exercise sovereignty over the same territory instead of each controlling a separate portion.

Can You Visit Pheasant Island?

No. Pheasant Island is not open to ordinary visitors. Public access to the island is restricted, so travelers cannot simply take a boat or walk onto the island as they would at a normal tourist destination.

You can, however, see Pheasant Island from the French or Spanish riverbanks. Its small size and protected status mean that viewing it from the surrounding area is generally the practical way to experience the island.

This makes Pheasant Island very different from divided islands such as Saint Martin or Usedom, where travelers can freely cross between the two countries.

For most visitors, the attraction is therefore not exploring the island itself. It is seeing the unusual territory from outside and learning about its remarkable history and shared sovereignty.

Why Are Some Islands Divided Between Two Countries?

An island can be divided between two countries for many historical and political reasons. In most cases, the present-day border is the result of events that happened long before the modern countries existed in their current form.

Colonial rule, wars, treaties, and changing territorial claims have all shaped the political map of divided islands. The border may reflect an old agreement, a former colonial boundary, or a political settlement reached after a conflict.

Colonial Borders

European colonial powers often divided territories without regard to the cultural or geographic boundaries that already existed.

When colonial possessions later became independent countries, some of these old boundaries became international borders. This is one reason an island can contain two countries even though there is no obvious natural feature separating them.

Timor provides a good example. Portuguese and Dutch colonial control divided the island into eastern and western spheres, creating the historical basis for the modern boundary between Timor-Leste and Indonesia.

Similarly, colonial-era arrangements played an important role in shaping the division of New Guinea between Indonesia and Papua New Guinea.

Wars and Territorial Agreements

Wars have frequently changed control over islands and territories. When conflicts end, the victorious and defeated sides may negotiate new boundaries or accept territorial changes.

These agreements can divide an island that was previously controlled by a single power.

The political division of Ireland, for example, developed through a long period of conflict and constitutional change involving British rule and the Irish independence movement. The resulting political boundary remains one of the most significant divisions on a European island.

Treaties and International Boundaries

Treaties are among the most important tools used to establish or formally recognize international borders.

Countries can negotiate where a boundary should run, sometimes following natural features such as rivers and mountains, and sometimes creating an entirely surveyed line across an island.

The division of Saint Martin between France and the Netherlands dates back to the Treaty of Concordia, signed in 1648. The agreement established the basic division that still exists today.

Treaties can also produce surprisingly unusual borders. On Märket, the boundary between Finland and Sweden takes an unusual shape because of the island’s historical lighthouse and the need to accommodate the territorial boundary.

Historical Claims and Political Changes

Borders do not always remain unchanged. Political control can shift through independence movements, territorial transfers, constitutional changes, or agreements between neighboring states.

A former colonial boundary may become an international border after independence. A territory can also change countries following a war or diplomatic settlement.

Usedom, divided between Germany and Poland, demonstrates how major political changes can redraw borders while leaving the physical island exactly where it has always been.

The landscape does not move when a border changes. A political line can simply be redrawn across the same mountains, forests, rivers, and settlements.

How Are Islands Divided Between Two Countries?

Countries can share the same geographic island in different ways. In some cases, an international land border physically crosses the island. In others, different parts of the island fall under separate governments. A few rare islands have arrangements where two countries share sovereignty rather than dividing the land permanently.

These distinctions matter because not every island shared by two countries is divided in exactly the same way.

A Land Border Runs Across the Island

The simplest arrangement is an international land border crossing a single geographic island.

The island remains one continuous landmass, but a surveyed political boundary separates the territories of two countries. Each country exercises sovereignty on its respective side of the border.

Timor is a clear example. Indonesia controls the western portion of the island, while Timor-Leste controls most of the eastern portion.

Sebatik Island provides another example. The Indonesia–Malaysia border runs across the island, separating the Malaysian territory in the north from Indonesian territory in the south.

In both cases, the border is a political boundary rather than a natural break in the island itself.

Different Parts of the Island Have Different Governments

Another situation occurs when different parts of a single island are administered by separate governments.

The most prominent example is Hispaniola. Haiti occupies the western part of the island, while the Dominican Republic occupies the eastern portion.

There is a formal international border between the two countries, so each government exercises authority over its own territory.

This arrangement can affect everything from laws and immigration to currency, infrastructure, and travel. Yet geographically, Hispaniola remains one island.

Sovereignty Is Shared or Unusually Arranged

A much rarer situation occurs when two countries share sovereignty over the same territory, rather than dividing the island into separate national sections.

Pheasant Island, located in the Bidasoa River between France and Spain, is a notable example. France and Spain share sovereignty over the tiny island, with administrative responsibility alternating between the two countries.

There is therefore no permanent French half and Spanish half separated by an international border.

This is why Pheasant Island is better described as a shared-sovereignty island than a conventionally divided island.

Are There Lake Islands Shared by Two Countries?

Yes. An island inside a lake can belong to two countries if an international boundary crosses the island.

This unusual situation occurs when a national border passes through a lake and continues across one of its islands. The island remains one geographic landmass, but different parts fall under the jurisdiction of different countries.

How Can This Happen?

International borders do not always follow coastlines or major rivers. In some places, a boundary crosses a lake and continues across nearby islands.

This can create tiny pieces of territory belonging to different countries on the same island. The result is similar to a divided sea island, except the island is surrounded by freshwater rather than the sea.

Boundary Lake: An Unusual Example

One example is Boundary Lake, on the Canada–United States border between Manitoba and North Dakota.

Two islands in the lake are divided by the international boundary. The western island is particularly tiny, measuring only about 1.1 hectares. This makes it an unusual example of a very small landmass split between two countries.

Are There Other Divided Lake Islands?

Yes. There are several.

Canada and the United States divide islands in places including Lake Memphremagog and Lake of the Woods. Other divided lake islands occur along the Canada–US border in Montana, Saskatchewan, North Dakota, and other border regions.

Norway and Sweden provide another remarkable example. Their international border divides numerous small lake islands, including several very small islands and islets.

Why Are Lake Islands Interesting?

Lake islands show that divided islands are not limited to oceans and seas.

A country can share an island with another country even when that island is surrounded entirely by freshwater. In some cases, the divided island is so small and remote that few people ever visit it.

Why Is There No Single Smallest Divided Island?

The answer depends on how the question is defined.

If we are talking about an inhabited island, the answer is Saint Martin, the Caribbean island divided between France and the Netherlands. At about 87 square kilometres, it is recognized by Guinness World Records as the smallest populated island shared by two nations.

But if we include tiny, uninhabited sea islands, the answer changes dramatically.

Märket: The Smallest Sea Island Shared by Two Countries

Märket, a tiny rocky islet in the Baltic Sea, is shared by Finland and Sweden. It covers only about 3.3 hectares, or approximately 0.033 square kilometres.

Its tiny size makes Märket vastly smaller than Saint Martin. It is also famous for its unusual international boundary, which bends around the historic lighthouse on the islet.

Märket is therefore commonly described as the smallest sea island shared by two countries.

Why Is Saint Martin Often Called the Smallest?

The apparent contradiction comes from the definition being used.

Saint Martin is inhabited and divided between the French territory of Saint-Martin and Sint Maarten, a constituent country within the Kingdom of the Netherlands. The French local government describes it as the world’s smallest landmass shared by two independent states, while Guinness specifically identifies it as the smallest populated island shared by two nations.

Märket, by contrast, is a tiny uninhabited sea island.

There are also even smaller border islands and islets that can complicate claims about the absolute smallest. Guinness notes examples such as Koiluoto and points out that definitions of what constitutes an island can affect the record.

So, Which Is the Smallest?

For clarity, the safest way to state the answer is:

Smallest inhabited island shared by two countries: Saint Martin — France and the Netherlands

Smallest sea island commonly described as shared by two countries: Märket — Finland and Sweden

This distinction matters because calling either one simply “the smallest island shared by two countries” without qualification can be misleading.

For IslandsAndIslets.com, it is better to explain the different definitions than to repeat an absolute record that may depend on how an island or sovereign state is defined.

What Types of Islands Can Be Shared by Two Countries?

An island shared by two countries does not have to be a large ocean island. International borders can divide islands in seas, rivers, and lakes, creating some remarkably unusual political boundaries.

The way countries share an island can also differ. In most cases, an international border divides the land into separate territories. In a few unusual cases, the countries share sovereignty over the entire island.

Sea and Ocean Islands

Most well-known divided islands are surrounded by seawater.

Hispaniola, New Guinea, Timor, Ireland, and the main island of Tierra del Fuego are large examples. Their territories are divided between two countries, with an international boundary separating the respective jurisdictions.

Smaller sea islands and islets can also be divided. Märket, shared by Finland and Sweden, is one of the best-known examples because of its unusual border and tiny size.

River Islands

An international boundary can also divide an island located within a river.

Pheasant Island, in the Bidasoa River between France and Spain, is a particularly unusual example. It is not divided into a French side and a Spanish side. Instead, France and Spain share sovereignty over the entire island, with administration alternating between the two countries.

This makes Pheasant Island different from most of the other islands in this article.

Lake Islands

Yes, even islands surrounded by freshwater can be shared by two countries.

International borders cross several lake islands around the world. Examples occur along the borders of Canada and the United States, Finland and Norway, Finland and Sweden, and other neighboring countries.

Some are extremely small and remote. Their existence also makes the question of the world’s smallest divided island much harder to answer.

Islands With Shared Sovereignty

A much rarer arrangement occurs when two countries share sovereignty rather than dividing the island into separate national territories.

Pheasant Island is the clearest example in this article. France and Spain exercise sovereignty over the same small island under an unusual alternating administration system.

This is sometimes described as a condominium in international law. It should not be confused with an island that is permanently divided by an international border.

Where Can You See an International Border on an Island?

An international border does not always look like a fence or checkpoint. On some divided islands, you can see a border marker, monument, road crossing, or even an unusual line through the landscape.

In other places, the boundary is almost invisible.

Here are some of the most interesting examples.

Märket: An Unusual Border on a Tiny Island

Märket, shared by Finland and Sweden, has one of the world’s most unusual island borders.

The international boundary zigzags across the tiny rocky islet rather than following a simple straight line. The unusual shape developed around the lighthouse, which was built on the wrong side of the original boundary. The border was later adjusted so the lighthouse could remain in Finland.

The boundary turning points are marked on the rocks, although there are no normal border formalities for people on the islet.

Sebatik Island: A Border Running Across Everyday Life

On Sebatik Island, the Indonesia–Malaysia border runs roughly across the island.

The northern part belongs to Malaysia, while the southern part belongs to Indonesia. Unlike a heavily fortified international frontier, much of the boundary has historically been marked by concrete boundary posts rather than a continuous wall or fence.

The border can therefore pass through areas where people live and work on both sides.

That makes Sebatik one of the clearest examples of an international boundary dividing a single inhabited island.

Usedom: A Border You Can Cross Easily

Usedom, divided between Germany and Poland, provides a very different experience.

The international border is visible in places, including marked crossings and border infrastructure. But because Germany and Poland are both part of the Schengen Area, travelers can generally move between the two sides without routine internal border checks.

The island therefore demonstrates how an international border can remain politically important while becoming almost invisible in everyday travel.

Saint Martin: A Border With a Monument

On Saint Martin, the French–Dutch boundary is much less dramatic than many international borders.

The Concordia Monument marks the historic division between the French and Dutch sides of the island. It stands near the border between Cole Bay and Marigot.

There is no imposing barrier separating the two sides. Visitors can move around the island and encounter the boundary as part of the normal landscape.

Pheasant Island is a completely different case.

The small island lies in the Bidasoa River between France and Spain, but it is not divided into a French half and a Spanish half. Instead, France and Spain share sovereignty, with administration alternating between the two countries.

There is therefore no conventional international border line running across the island.

This makes Pheasant Island an important reminder that an “island shared by two countries” does not always mean that a visible boundary divides the land.

There is no single appearance.

An international border on an island can be:

Clearly marked with boundary posts, signs, or monuments.

Unusual in shape, as on Märket.

Easy to cross, as on Usedom and Saint Martin.

Barely visible, as on parts of Sebatik.

Absent as a dividing line, in special shared-sovereignty cases such as Pheasant Island.

That variety is one of the reasons divided islands are so interesting. The political boundary can be highly visible—or almost impossible to notice—while still separating different jurisdictions.

Islands Shared by Two Countries vs. Three Countries

Some islands are divided among three or more countries. Borneo is the clearest example, with Indonesia, Malaysia, and Brunei sharing the island. It belongs in a broader multi-country island category, not this main list.

An island shared by exactly two countries has territory or sovereignty belonging to two states. Hispaniola, New Guinea, Timor, Saint Martin, and Sebatik are examples.

Can You Visit an Island Shared by Two Countries?

Yes, in many cases you can visit an island shared by two countries. But the experience depends on how the border works and what travel rules apply.

Some divided islands allow visitors to move between both sides with little difficulty. Others have formal border crossings, immigration checks, or restrictions on where visitors can go.

The important point is that an island being geographically connected does not mean its entire territory has the same travel rules.

Islands With Easy Cross-Border Travel

Some divided islands are surprisingly easy to explore across the international boundary.

Saint Martin is the clearest example. The island is divided between French Saint-Martin and Dutch Sint Maarten, but visitors can travel between the two sides without a conventional land border checkpoint. The political boundary is still real, even though it is not usually experienced like a heavily controlled international border.

Usedom, divided between Germany and Poland, offers another easy example. Both countries are part of the Schengen Area, where internal border controls are generally absent. Visitors can move between the German and Polish parts of the island without passing through a traditional passport checkpoint.

These islands can therefore feel like a single travel destination despite having an international border running across them.

Islands Where Border Rules Matter

Other divided islands require much more attention to immigration rules.

On Hispaniola, for example, crossing from the Dominican Republic into Haiti means crossing an international border between two separate countries. Travelers must use authorized border crossings and comply with the immigration requirements of the countries involved.

The same principle applies to islands such as Timor, where Indonesia and Timor-Leste have an international land border. A traveler cannot simply cross the boundary anywhere on the island because the two countries have separate immigration systems and designated crossing arrangements.

Your passport, visa requirements, entry permissions, and current border conditions can therefore matter just as much as they would at any other international land border.

Travel rules can also change. Always check current government travel and immigration information before planning a cross-border journey.

Islands You Should Not Treat as One Destination

A divided island may be geographically continuous but politically separate.

That distinction matters when planning a trip. Saint Martin and Sint Maarten can be explored together relatively easily, while other divided islands may require a deliberate international border crossing.

Some islands also contain remote or restricted border areas. Märket, for example, is tiny and remote, so its unusual international boundary does not make it a conventional two-country tourist destination.

Pheasant Island is an even stronger example. It is shared by France and Spain under an unusual sovereignty arrangement, but ordinary visitors cannot simply land on the island and explore it.

So, before treating a divided island as one destination, check three things:

Can you legally cross the internal border?

Do you need a visa or immigration clearance?

Is the border area or island itself open to visitors?

The most interesting divided islands are not always the easiest to visit. Some are excellent travel destinations, while others are better understood from viewpoints, maps, or surrounding areas.

Other Small Islands Divided by International Borders

The best-known divided islands are only part of the story. Around the world, international borders also cross tiny islands, remote islets, and unusual landforms that rarely appear in ordinary travel guides.

Some are important because of their history. Others are remarkable simply because of their tiny size or unusual geography.

Hans Island — Canada and Denmark

Hans Island is a tiny, uninhabited island in the Nares Strait between Greenland and Canada.

For decades, Canada and Denmark disputed sovereignty over the island. In 2022, the two countries reached an agreement that divided Hans Island between Canada and the Kingdom of Denmark, represented by Greenland.

The agreement created a land boundary on an island that had previously been the subject of a long-running territorial dispute.

Hans Island is therefore an interesting example of how a disputed island can eventually become a formally divided island.

Kataja — Finland and Sweden

Kataja is a small island in the northern Baltic Sea, divided between Finland and Sweden.

Its history is particularly unusual. The modern island formed after post-glacial land uplift caused two previously separate islands to join together. The international boundary that had separated the original islands now crosses the combined landmass.

The result is an island that became divided partly because the landscape itself changed over time.

Koiluoto — Finland and Russia

Koiluoto is a tiny island in the Gulf of Finland divided between Finland and Russia.

The island is only about 0.03 square kilometres and is roughly 200 metres long. Both portions lie within border zones and are off-limits to the general public.

Koiluoto is a useful reminder that a divided island does not have to be large, inhabited, or accessible to travelers.

Tiny Lake Islands Along International Borders

Some of the world’s most unusual divided islands are not in the sea at all.

Several tiny lake islands are divided by international borders. Examples occur along the borders of Finland and Russia, Finland and Norway, Sweden and Norway, and Canada and the United States.

Some are so small that they have little practical importance beyond their unusual political geography.

Frequently Asked Questions

What islands are shared by two countries?

Several islands are divided between two countries, including Hispaniola, Saint Martin, New Guinea, Timor, Ireland, the main island of Tierra del Fuego, Sebatik Island, Märket, and Usedom. The political arrangements differ from island to island.

How many islands are divided between two countries?

There is no single universally accepted number. The total depends on how researchers define an island, an islet, a country, and shared sovereignty. Several major inhabited islands are divided between exactly two countries, while numerous smaller border islands and islets also exist.

Which island is shared by France and the Netherlands?

Saint Martin is shared by France and the Netherlands. The northern part is the French collectivity of Saint-Martin, while the southern part is Sint Maarten, a constituent country within the Kingdom of the Netherlands.

Which island is shared by Haiti and the Dominican Republic?

Hispaniola is shared by Haiti and the Dominican Republic. Haiti occupies the western part of the island, while the Dominican Republic occupies the eastern part.

Which island is divided between Indonesia and Papua New Guinea?

New Guinea is divided between Indonesia and Papua New Guinea. Indonesia controls the western portion, while Papua New Guinea occupies the eastern portion.

What island is shared by Indonesia and Malaysia?

Sebatik Island is divided between Indonesia and Malaysia. The international border runs across the island, with Malaysian territory in the north and Indonesian territory in the south.

Are there islands shared by three countries?

Yes. Borneo is the best-known example. It is divided among Indonesia, Malaysia, and Brunei, making it different from the two-country islands covered in the main list.

What is the smallest island shared by two countries?

The answer depends on the definition. Saint Martin is recognized as the smallest inhabited island shared by two nations, while tiny islands such as Märket are much smaller but uninhabited. Claims about the absolute smallest can vary depending on which islands and definitions are included.

Can you visit islands shared by two countries?

Yes, but travel conditions vary. Some islands, such as Saint Martin and Usedom, allow relatively easy movement between their two sides, while others have formal border crossings or restricted areas.

Why are some islands divided between countries?

Divided islands usually result from historical and political events. Colonial boundaries, wars, treaties, territorial agreements, and later political changes have all created international borders across islands.

Is Ireland an island shared by two countries?

Ireland can be described geographically as an island containing two political jurisdictions. The Republic of Ireland is a sovereign state, while Northern Ireland is part of the United Kingdom.

Is Pheasant Island shared by France and Spain?

Yes, but Pheasant Island is unusual. France and Spain share sovereignty over the small island, with administration alternating between the two countries. It is not a conventional island permanently divided into French and Spanish territories, and ordinary visitors cannot freely access it.

Conclusion

Islands shared by two countries are among the most fascinating examples of political geography. They can be found in oceans, seas, rivers, and other waterways around the world.

From large islands such as Hispaniola and New Guinea to smaller border islands and unusual river islands, each example has a different story. Some were divided by treaties, while others reflect colonial boundaries, wars, or centuries of political change.

For travelers, these islands offer another interesting perspective. Some allow easy movement between two countries, while others have formal border crossings or restricted access.

What makes them remarkable is the contrast between geography and politics. Nature creates one island, but history can divide it between two countries.

Whether the border runs through a busy town, across a remote landscape, or along a quiet river, these islands show that international boundaries can appear in some of the most unexpected places on Earth.

• Strangest Islands in the World — use Pheasant Island and other unusual political islands as supporting links.

 

Last Updated: September 6, 2026