Sevastopol (/ˌsɛvəˈstoʊpəl, sɪˈvæstəpoʊl/ SEV-ə-STOH-pəl, siv-AST-ə-pohl), sometimes written Sebastopol, is the largest city in Crimea and a major port on the Black Sea. Due to its strategic location and the navigability of the city's harbours, Sevastopol has been an important port and naval base throughout its history. Since the city's founding in 1783, it has been a major base for Russia's Black Sea Fleet. During the Cold War of the 20th century, it was a closed city. The total administrative area is 864 square kilometres (334 sq mi) and includes a significant amount of rural land. The urban population, largely concentrated around Sevastopol Bay, is 479,394, and the total population is 547,820.

Sevastopol, along with the rest of Crimea, is internationally recognised as part of Ukraine, and under the Ukrainian legal framework, it is administratively one of two cities with special status (the other being Kyiv). However, it has been occupied by Russia since 27 February 2014, before Russia annexed Crimea on 18 March 2014 and gave it the status of a federal city of Russia. Both Ukraine and Russia consider the city administratively separate from the Autonomous Republic of Crimea and the Republic of Crimea, respectively. The city's population has an ethnic Russian majority and a substantial minority of Ukrainians and Crimean Tatars.

Sevastopol's unique naval and maritime features have been the basis for a robust economy. The city enjoys mild winters and moderately warm summers, characteristics that help make it a popular seaside resort and tourist destination, mainly for visitors from the former Soviet republics. The city is also an important centre for marine biology research. In particular, the military has studied and trained dolphins in the city for military use since the 1960s.

The name of Sevastopolis was originally chosen following the same etymological trend as other cities in the Crimean peninsula; it was intended to express its ancient Greek origins. It is a compound of the Greek adjective, σεβαστός (sebastós, Byzantine Greek pronunciation: [sevasˈtos]; 'venerable') and the noun πόλις (pólis, 'city'). Σεβαστός is the traditional Greek equivalent (see Sebastian) of the Roman honorific Augustus, originally given to the first emperor of the Roman Empire, Augustus and later awarded as a title to his successors.

The city was probably named after Empress ("Augusta") Catherine II of the Russian Empire who founded Sevastopol in 1783. She visited the city in 1787, accompanied by Joseph II, the Emperor of Austria, and other foreign dignitaries.

In the west of the city, there are well-preserved ruins of the ancient Greek port city of Chersonesos, founded in the 5th century BC by settlers from Heraclea Pontica. This name means "peninsula", reflecting its immediate location. It is not related to the ancient Greek name for the Crimean Peninsula as a whole: Chersonēsos Taurikē ("the Taurian Peninsula").

The name of the city is spelled as:

Chersonesus founded in 6th century BC
Hellenic Colonies 6th century BC – 480 BC
Bosporan Kingdom 480 BC – 107 BC
Kingdom of Pontus 107 BC – 63 BC
Roman Republic 63 BC – 27 BC
Roman Empire 27 BC – 330
Byzantine Empire 330 – 1204
Empire of Trebizond 1204 – 1461
Principality of Theodoro 1461 – 1475
Crimean Khanate 1475 – 1783 (Ottoman vassal from 1478 to 1774)
Russian Empire 1783 – 1917
Founded as Sevastopol in 1783
Russian Republic 1917
Russian SFSR (Soviet Union from 1922) 1917 – 1942
Nazi Germany 1942 – 1944 (de facto)
Russian SFSR (Soviet Union) 1944 – 1954
Ukrainian SSR (Soviet Union) 1954 – 1991
Ukraine 1991 – 2014 (de facto; de jure – 1991–present)
Russian Federation 2014 – present (de facto)