Zagreb ( ZAH-greb, ZAG-reb, zah-GREB, Croatian: [zǎːɡreb] (listen)) is the capital and largest city of Croatia. It is in the northwest of the country, along the Sava river, at the southern slopes of the Medvednica mountain. Zagreb stands near the international border between Croatia and Slovenia at an elevation of approximately 122 m (400 ft) above sea level. The population of the Zagreb urban agglomeration is 1,071,150, approximately a quarter of the total population of Croatia, while at the 2021 census the city itself had a population of 767,131.

Zagreb is a city with a rich history dating from Roman times. The oldest settlement in the vicinity of the city was the Roman Andautonia, in today's Ščitarjevo. The historical record of the name "Zagreb" dates from 1134, in reference to the foundation of the settlement at Kaptol in 1094. Zagreb became a free royal city in 1242. In 1851 Janko Kamauf became Zagreb's first mayor.

Zagreb has special status as a Croatian administrative division - it comprises a consolidated city-county (but separate from Zagreb County), and is administratively subdivided into 17 city districts. Most of the city districts lie at a low elevation along the valley of the river Sava, but northern and northeastern city districts, such as Podsljeme and Sesvete districts are situated in the foothills of the Medvednica mountain, making the city's geographical image quite diverse. The city extends over 30 km (19 mi) east-west and around 20 km (12 mi) north-south.

Zagreb ranks as a global city, with a Beta − rating from the Globalization and World Cities Research Network.

The transport connections, the concentration of industry, scientific, and research institutions and industrial tradition underlie its leading economic position in Croatia. Zagreb is the seat of the central government, administrative bodies, and almost all government ministries. Almost all of the largest Croatian companies, media, and scientific institutions have their headquarters in the city. Zagreb is the most important transport hub in Croatia: here Central Europe, the Mediterranean and Southeast Europe meet, making the Zagreb area the centre of the road, rail and air networks of Croatia. It is a city known for its diverse economy, high quality of living, museums, sporting, and entertainment events. Major branches of Zagreb's economy include high-tech industries and the service sector.