Odesa (also spelled Odessa) is the third most populous city and municipality in Ukraine and a major seaport and transport hub located in the south-west of the country, on the northwestern shore of the Black Sea. The city is also the administrative centre of the Odesa Raion and Odesa Oblast, as well as a multiethnic cultural centre. As of January 2021, Odesa's population was approximately 1,010,537. On January 25, 2023, its historic city centre was declared a World Heritage Site and added to the List of World Heritage in Danger by the UNESCO World Heritage Committee in recognition of its influence on cinema, literature, and the arts. The declaration was made in response to the bombing of Odesa during the 2022 Russian invasion of Ukraine, which has damaged or destroyed buildings across the city.

In classical antiquity a large Greek settlement existed at its location. The first chronicle mention of the Slavic settlement-port of Kotsiubijiv, which was part of the Grand Duchy of Lithuania, dates back to 1415, when a ship was sent from here to Constantinople by sea. After the Grand Duchy lost control, the port and its surroundings became part of the domain of the Ottoman Empire in 1529, under the name Hacibey, and remained in it until the Ottomans' defeat in the Russo-Turkish War (1787–1792).

In 1794, the modern city of Odesa was founded by a decree of the Russian empress Catherine the Great. From 1819 to 1858, Odesa was a free port. During the Soviet period, it was an important trading port and a naval base.

During the 19th century, Odesa was the fourth largest city of the Russian Empire, after Moscow, Saint Petersburg and Warsaw. Its historical architecture is more Mediterranean than Russian, having been heavily influenced by French and Italian styles. Some buildings are built in a mixture of different styles, including Art Nouveau, Renaissance and Classicist.

Odesa is a warm-water port. The city of Odesa hosts both the Port of Odesa and Port Pivdennyi, a significant oil terminal situated in the city's suburbs. Another notable port, Chornomorsk, is located in the same oblast, to the south-west of Odesa. Together they represent a major transport hub integrating with railways. Odesa's oil and chemical processing facilities are connected to the Russian and other European networks by strategic pipelines. In 2000, the Quarantine Pier at Odesa Commercial Sea Port was declared a free port and free economic zone for a period of 25 years.