Mount Vesuvius ( viss-OO-vee-əs; Italian: Vesuvio [veˈzuːvjo, -ˈsuː-]; Neapolitan: 'O Vesuvio [o vəˈsuːvjə], also 'A muntagna or 'A montagna; Latin: Vesuvius [wɛˈsʊwi.ʊs], also Vesevius, Vesvius or Vesbius) is a somma-stratovolcano located on the Gulf of Naples in Campania, Italy, about 9 km (5.6 mi) east of Naples and a short distance from the shore. It is one of several volcanoes forming the Campanian volcanic arc. Vesuvius consists of a large cone partially encircled by the steep rim of a summit caldera, resulting from the collapse of an earlier, much higher structure.

The eruption of Mount Vesuvius in AD 79 destroyed the Roman cities of Pompeii, Herculaneum, Oplontis, Stabiae, and several other settlements. The eruption ejected a cloud of stones, ashes and volcanic gases to a height of 33 km (21 mi), erupting molten rock and pulverized pumice at the rate of 6×10⁵ cubic metres (7.8×10⁵ cu yd) per second. More than 1,000 people are thought to have died in the eruption, though the exact toll is unknown. The only surviving eyewitness account of the event consists of two letters by Pliny the Younger to the historian Tacitus.

Vesuvius has erupted many times since. It is the only volcano on Europe's mainland to have erupted in the last hundred years. It is regarded as one of the most dangerous volcanoes in the world because 3,000,000 people live near enough to be affected by an eruption, with at least 600,000 in the danger zone. This is the most densely populated volcanic region in the world. Eruptions tend to be violent and explosive; these are known as Plinian eruptions.