Bakı (bəkē´) or Baku (bəkōō´), city (1991 pop. 1,782,000), capital of Azerbaijan, on the Caspian Sea. Greater Bakı includes almost the whole Absheron peninsula, on which Bakı proper is situated; the city is located below sea level. The city was a leading Soviet industrial and cultural center and until World War II was the USSR's chief petroleum center. It handled one of the greatest volumes of freight (mainly oil and oil products) of any Soviet port. Oil drilling (especially on the Absheron peninsula and offshore) is the major economic activity. Bakı has many oil refineries and factories that produce oil-field equipment, and is one terminus of a pipeline that extends to near Ceyhan, Turkey. Other important industries include shipbuilding and the processing of food and tobacco. Many of Bakı's people are Azeri (46%), but there are large numbers of Russians and Armenians.

The city was first mentioned in a 9th-century chronicle; but as early as the 6th cent. BC oil and gas wells in the area were worshiped, and shrines were made of constantly burning fires. Bakı was a great medieval trade and craft center. It flourished in the 15th cent. under the independent Shirvan shahs and from 1509 to 1723 under Persian rule. Captured by Peter I in 1723, it was returned to Persia in 1735. Russia annexed it definitively in 1806. Oil production began in the late 19th cent. Taken by the Bolsheviks in 1917, the city was occupied during the next two years by the White Army and its foreign allies (mainly Britain). From 1918 to 1920, Bakı belonged to the independent, anti-Bolshevik Azerbaijan republic. In Jan., 1990, Bakı was the scene of fierce fighting as Soviet forces put down Azeri militants who had declared independence. Since independence (1991) Azerbaijan's economic growth has been disproportionately concentrated in Bakı.

The Old City, comprising the 13th-century fortress of Bad-Kube, has narrow, winding streets, several mosques, and the 17th-century palace of the khans of Bakı, who were vassals of the Persian shahs. The mosque of Synyk-Kala dates from the 11th cent. and the Maiden's Tower from the 12th. In the European-style New City are the university (est. 1920), the Azerbaijan Academy of Sciences, and many other educational and cultural institutions. In recent years new construction—including the Heydar Aliyev Center (2012), Baku Crystal Hall (2012), Flame Towers (2013)—has transformed the city. The Fire Temple, 16 mi (26 km) from the city, still taps an ancient natural gas seepage and was a place of worship for Zoroastrians.