Sevastopol ( se-və-STOH-pəl, sə-VAS-tə-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, and it was previously a closed city during the Cold War. 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.

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.