Sofia (Bulgarian: София, pronounced [ˈsɔfijɐ] ( listen)) is the capital and largest city of Bulgaria. Sofia is located at the foot of Mount Vitosha in the western part of the country. It occupies a strategic position at the centre of the Balkan Peninsula. Sofia's history spans 2,400 years. Its ancient name Serdica derives from the local Celtic tribe of the serdi who established the town in the 5th century BC. It remained a relatively small settlement until 1879, when it was declared the capital of Bulgaria.

Sofia is the 15th largest city in the European Union with a population of around 1.2 million people, or 1,166,000 in the city proper. More than 95% of all inhabitants are ethnic Bulgarian, making it the most ethnically homogenous city in Bulgaria.

Sofia has been ranked by the Globalization and World Cities Research Network as a beta city. Many of the major universities, cultural institutions, and businesses of Bulgaria are concentrated in Sofia.