The Mediterranean Sea ( MED-ih-tə-RAY-nee-ən) is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Southern Europe and Anatolia, on the south by North Africa, and on the east by the Levant in Western Asia. The Mediterranean has played a central role in the history of Western civilization. Geological evidence indicates that around 5.9 million years ago the Mediterranean was cut off from the Atlantic and was partly or completely desiccated over a period of some 600,000 years during the Messinian salinity crisis before being refilled by the Zanclean flood about 5.3 million years ago.

The Mediterranean Sea covers an area of about 2,500,000 km² (970,000 sq mi), representing 0.7% of the global ocean surface, but its connection to the Atlantic via the Strait of Gibraltar—the narrow strait that connects the Atlantic Ocean to the Mediterranean Sea and separates the Iberian Peninsula in Europe from Morocco in Africa—is only 14 km (9 mi) wide. The Mediterranean Sea encompasses a vast number of islands, some of them of volcanic origin. The two largest islands, in both area and population, are Sicily and Sardinia.

The Mediterranean Sea has an average depth of 1,500 m (4,900 ft) and the deepest recorded point is 5,109 m (16,762 ft) ±1 m (3 ft) in the Calypso Deep in the Ionian Sea. It lies between latitudes 30° and 46° N and longitudes 6° W and 36° E. Its west–east length, from the Strait of Gibraltar to the Gulf of Alexandretta, on the southeastern coast of Turkey, is about 4,000 kilometres (2,500 mi). The north–south length varies greatly between different shorelines and whether only straight routes are considered. Also including longitudinal changes, the shortest shipping route between the multinational Gulf of Trieste and the Libyan coastline of the Gulf of Sidra is about 1,900 kilometres (1,200 mi). The water temperatures are mild in winter and warm in summer and give name to the Mediterranean climate type due to the majority of precipitation falling in the cooler months. Its southern and eastern coastlines are lined with hot deserts not far inland, but the immediate coastline on all sides of the Mediterranean tends to have strong maritime moderation.

The sea was an important route for merchants and travellers of ancient times, facilitating trade and cultural exchange between the peoples of the region. The history of the Mediterranean region is crucial to understanding the origins and development of many modern societies. The Roman Empire maintained nautical hegemony over the sea for centuries and is the only state to have ever controlled all of its coast.

The countries surrounding the Mediterranean in clockwise order are Spain, France, Monaco, Italy, Slovenia, Croatia, Bosnia and Herzegovina, Montenegro, Albania, Greece, Turkey, Syria, Lebanon, Israel, Palestine, Egypt, Libya, Tunisia, Algeria, and Morocco; Malta and Cyprus are island countries in the sea. In addition, Gibraltar and Ceuta, have coastlines on the sea. The drainage basin encompasses a large number of other countries, the Nile being the longest river ending in the Mediterranean Sea.