Lisbon (Portuguese: Lisboa; Portuguese pronunciation: [liʒˈboɐ]) is the capital and largest city of Portugal. It is considered an alpha global city and is the seat of the district of Lisbon and the main city of the Lisbon region. Its municipality, which matches the city proper and excludes the larger continuous conurbation, has a municipal population of 564,477 in 84.8 km (33 sq mi), while the Lisbon Metropolitan Area in total has around 2.8 million inhabitants, and 3.34 million people live in the broader agglomeration of Lisbon Metropolitan Region (includes cities ranging from Leiria to Setúbal).

Due to its economic output, standard of living, and market size, the Grande Lisboa (Greater Lisbon) subregion is considered the second most important financial and economic centre in the Iberian Peninsula. The Lisbon region is the wealthiest region in Portugal and it is well above the European Union's GDP per capita average – it produces 37% of the Portuguese GDP. It is also the political centre of the country, as seat of government and residence of the Head of State.

Julius Caesar made it a municipium called Felicitas Julia, adding to the name Olissipo. Ruled by a series of Germanic tribes from the 5th century, it was captured by Moors in the 8th century. In 1147, the Crusaders under Afonso Henriques reconquered the city for the Christians and since then it has been a major political, economic and cultural center of Portugal. Unlike most capital cities, Lisbon's status as the capital of Portugal has never been granted or confirmed officially – by statute or in written form. Its position as the capital has formed through constitutional convention, making its position as de facto capital a part of the Constitution of Portugal.

Lisbon hosts two agencies of the European Union, namely, the European Monitoring Centre for Drugs and Drug Addiction (EMCDDA) and the European Maritime Safety Agency (EMSA). The Community of Portuguese Language Countries (CPLP), is also headquartered in Lisbon.