In political geography, an enclave is a country or part of a country lying wholly within the boundaries of another country. Many entities are both enclaves and exclaves, but the two are not synonymous.

The word enclave crept into the jargon of diplomacy rather late in English, in 1868, coming from French, the lingua franca of diplomacy, with a sense inherited from late Latin inclavatus meaning “shut in, locked up" (with a key, late Latin clavis). The word exclave is a logical extension created three decades later.

Enclaves may be created for a variety of historical, political or geographical reasons. Some areas have been left as enclaves simply due to changes in the course of a river. Since living in an enclave can be very inconvenient and many agreements have to be found by both countries over mail addresses, power supply or passage rights, enclaves tend to be eliminated and many cases that existed before have now been removed.

Many countries or parts of its are referred to as “enclaves” while this is not always the case. True enclaves are those territories where a country is sovereign, but which cannot be reached without entering one particular other country.

Some enclaves are countries in their own right, completely surrounded by another one, and therefore not exclaves (nor true enclaves), e.g. San Marino in Italy, Vatican City, Lesotho in South Africa.

In the world, there are more enclaves/exclaves than States. Europe has four significant areas of exclaves:

• Baarle-Hertog/Nassau with the Municipalities of Baarle-Hertog, a Belgian exclave in the Netherlands, and the Dutch Baarle-Nassau, which has some parcels of its territory inside the Belgian exclave;
• Campione d'Italia, an Italian Municipality  of Lombardy, occupying an enclave within the Swiss canton of Ticino, separated from the rest of Italy by Lake Lugano and mountains;
• Büsingen am Hochrhein, a German town entirely surrounded by the Swiss canton of Schaffhausen and south across the Rhine by Zürich and Thurgau;
• Llívia, a Spanish and Catalan enclave surrounded completely by French territory. It is situated in the French Pyrenees, East of Andorra and West of Perpignan.