To the west the Mediterranean Sea is connected to the Atlantic Ocean by the Strait of Gibraltar, which at its narrowest point is only 8 miles (13 km) wide and has a relatively shallow channel. To the northeast the Dardanelles, the Sea of Marmara, and the strait of the Bosporus link the Mediterranean Sea to the Black Sea. The Suez Canal connects it with the Red Sea to the southeast. The Mediterranean's greatest recorded depth is in the Ionian Basin south of Greece at 16,800 feet (5,121 m) below sea level.

A submarine ridge between the island of Sicily and the African coast divides the Mediterranean Sea into eastern and western parts. The western Mediterranean has three submarine basins separated from each other by submerged ridges, including from west to east, the Alborán, the Algerian, and the Tyrrhenian basins. The Ionian Basin (northwest of which is the Adriatic Sea) and the Levantine Basin (northwest of which is the Aegean Sea) compose the eastern part of the Mediterranean Sea. Majorca, Corsica, Sardinia, Sicily, Crete, Cyprus, and Rhodes are the largest islands in the Mediterranean.

The Mediterranean once was thought to be a remnant of the Tethys Sea, which formerly girdled the Eastern Hemisphere; it is now known to be a structurally younger basin. The sea's continental shelves are relatively narrow. The widest shelf, off the Gulf of Gabes (Qabis) on the eastern coast of Tunisia, extends 170 miles (275 km); the bed of the Adriatic Sea is also mostly continental shelf. The floor of the Mediterranean consists of sediments made up of lime, clay, and sand, under which is blue mud. The sea's coasts are generally steep, rocky, and deeply indented. The Rhône, Po, and Nile rivers have formed the only large deltas in the Mediterranean Sea. The continuous inflow of surface water from the Atlantic Ocean is the sea's major source of replenishment. The most constant component of circulation in the Mediterranean Sea is the current formed by this inflow from the Strait of Gibraltar along the north coast of Africa. The whole Mediterranean basin is tectonically active, and earthquakes are common.

The climate is characterized by mild, wet winters and hot, dry summers. The air flow into the Mediterranean is through gaps in the mountain ranges, except over its southern shores east of Tunisia. Much of North Africa rarely receives more than 10 inches (250 mm) of rainfall annually, whereas on the rugged Dalmatian coast of Croatia, some areas receive 100 inches (2,500 mm).

The low concentration of phosphates and nitrates, necessary for marine pastures, limits the quantity of marine life in the Mediterranean. Small-scale fishing operations predominate, with the most important species including hake, flounder, sole, turbot, sardine, anchovy, bluefin tuna, bonito, and mackerel; shellfish, corals, sponges, and seaweed are also harvested. Overexploitation of the sea's marine resources remains a serious problem.

Petroleum deposits have been found off Spain, Sicily, Libya, and Tunisia, and natural gas has been discovered in the Adriatic Sea. Specialty crops of the region include olives, citrus fruits, grapes, and cork. Tourism is a major source of income for many of the countries bordering the Mediterranean.