The Tyrrhenian Sea (tɪˈriːniːən,_-ˈreɪ-, ; Mar Tirreno mar tirˈrɛːno or -ˈreː-, Mer Tyrrhénienne mɛʁ tiʁenjɛn) is part of the Mediterranean Sea off the western coast of Italy. It is named for the Tyrrhenian people identified with the Etruscans of Italy.
The sea is bounded by the islands of Corsica and Sardinia (to the west), the Italian Peninsula (regions of Tuscany, Lazio, Campania, Basilicata, and Calabria) to the north and east, and the island of Sicily (to the south). The Tyrrhenian Sea also includes a number of smaller islands like Capri, Elba, Ischia, and Ustica.
The maximum depth of the sea is .
The Tyrrhenian Sea is situated near where the African and Eurasian Plates meet; therefore mountain chains and active volcanoes such as Mount Marsili are found in its depths. The eight Aeolian Islands and Ustica are located in the southern part of the sea, north of Sicily.
The International Hydrographic Organization defines the limits of the Tyrrhenian Sea as follows:
In the Strait of Messina: A line joining the North extreme of Cape Paci (15°42′E) with the East extreme of the Island of Sicily, Cape Peloro (38°16′N).
On the Southwest: A line running from Cape Lilibeo (West extreme of Sicily) to the South extreme of Cape Teulada (8°38′E) in Sardinia.
In the Strait of Bonifacio: A line joining the West extreme of Cape Testa (41°14′N) in Sardinia with the Southwest extreme of Cape Feno (41°23′N) in Corsica.
On the North: A line joining Cape Corse (Cape Grosso, 9°23′E) in Corsica, with Tinetto Island () and thence through Tino and Palmaria islands to San Pietro Point () on the coast of Italy.
There are four exits from the Tyrrhenian Sea (north to south):
The Tyrrhenian Basin is divided into two basins (or plains), the Vavilov plain and the Marsili plain. They are separated by the undersea ridge known as the Issel Bridge, after Arturo Issel.
The Tyrrhenian Sea is a back-arc basin that formed due to the rollback of the Calabrian slab towards South-East during the Neogene.