French Guiana, or Guyane in French, is an overseas department and region of France located on the northern coast of South America in the Guianas and the West Indies. Bordered by Suriname to the west and Brazil to the east and south, French Guiana covers a total area of 84,000 km² (32,000 sq mi) and a land area of 83,534 km² (32,253 sq mi). As of January 2025, it is home to 292,354 people.

French Guiana is the second-largest region of France, being approximately one-seventh the size of European France, and the largest outermost region within the European Union. It has a very low population density, with only 3.6 inhabitants per square kilometre (9.3/sq mi). About half of its residents live in its capital, Cayenne. Approximately 98.9% of French Guiana is covered by forests, much of it primeval rainforest. Guiana Amazonian Park, the largest national park in the European Union, covers 41% of French Guiana's territory.

Since December 2015, both the region and department have been ruled by a single assembly within the framework of a single territorial collectivity, the French Guiana Territorial Collectivity. This assembly, the French Guiana Assembly, replaced the former regional and departmental council, which were dissolved. The French Guiana Assembly is in charge of regional and departmental government. Its president is Gabriel Serville.

Fully integrated in the French Republic since 1946, French Guiana is a part of the European Union, and its official currency is the euro. A large part of French Guiana's economy depends on jobs and businesses associated with the presence of the Guiana Space Centre, now the European Space Agency's primary launch site near the equator. As elsewhere in France, the official language is standard French, but each ethnic community has its own language, of which French Guianese Creole, a French-based creole language, is the most widely spoken. French Guiana is the only territory on the continental mainland of the Americas that is still under the sovereignty of a European state.

The border between French Guiana and Brazil is the longest land border that France shares with another country, as well as one of only two borders which France shares with non-European states, the other being the border with Suriname in the west.

According to the Oxford English Dictionary, the name "Guyana" is an indigenous term meaning "land of many waters". The addition of the adjective "French" in most languages other than French is rooted in colonial times, when five such colonies (The Guianas) had been named along the coast, subject to differing powers: namely (from west to east) Spanish Guiana (now Guayana Region in Venezuela), British Guiana (now Guyana), Dutch Guiana (now Suriname), French Guiana, and Portuguese Guiana (now Amapá in Brazil). French Guiana and the two larger countries to the north and west, Guyana and Suriname, are still often collectively referred to as "the Guianas" and constitute one large landmass known as the Guiana Shield.

French Guiana was originally inhabited by indigenous people: Kalina, Lokono (part of the Arawak grouping), Galibi, Palikur, Teko, Wayampi and Wayana. The French attempted to create a colony there in the 16th century in conjunction with its settlement of some Caribbean islands, such as Guadeloupe and Saint-Domingue.

Prior to European colonization, the territory was originally inhabited by Native South Americans, most speaking the Arawak language, of the Arawakan language family. The people identified as Lokono. The first French establishment is recorded in 1503, but France did not establish a durable presence until colonists founded Cayenne in 1643.