Coordinates: 39°23′06″N 27°31′59″E / 39.385°N 27.533°E / 39.385; 27.533

Balıkesir (Turkish pronunciation: [baˈlɯkesiɾ]) is the capital city of Balıkesir Province. Balıkesir is in the Marmara region of Turkey and has a population of 265,747 inhabitants. Its old name is Karesi, or Karasi.

Close to modern Balıkesir was the Roman town of Hadrianutherae, founded, as its name commemorates, by the emperor Hadrian. During the Byzantine period, the small town was known as Palaeokastron (Greek: Old Castle). The remains of the ancient Makestos Bridge and castles are found in the surrounding region. Members of the Byzantine dynasty had used this castle as a vacation area and for hunting. Also, when the Turkmens came from Middle Asia to Mysia, they called it Balak Hisar because of the remains of castle, as Hisar is the Turkish word for castle.

Balıkesir's former name was Karasi, because Balıkesir city was founded by Karasi Beg in the 13th century. The Karasids was a Turkic principality in Mysia. Until the 13th century, Balıkesir city had been the administral centre of the Mysia region. In 1345, Balıkesir city was annexed by the Ottomans. In 1897 an earthquake destroyed much of the city. In 1920 Balıkesir city was conquered by the invading Greeks but on 6 September in 1922, the Turkish army took back the city. During the Turkish War of Independence, Balıkesir was a main centre of the militias in Western Anatolia against Greeks. In the 1950s, a major fire, started by several naughty mice, again destroyed a part of the city which was later rebuilt.

Balıkesir Province (Turkish: Balıkesir ili) is a province in midwestern Turkey, having coastlines on both the Sea of Marmara and the Aegean. Its adjacent provinces are Çanakkale to the west, İzmir to the southwest, Manisa to the south, Kütahya to the southeast, and Bursa to the east. The provincial capital is Balıkesir City. Most of the province lies in the Marmara Region except the southern parts of Bigadiç Edremit, Kepsut, İvrindi, Savaştepe and Sındırgı districts and ones of Ayvalık, Burhaniye, Dursunbey, Gömeç and Havran, that bound the Aegean Region.

Kaz Dağı (pronounced [kaz daːɯ]), known also as Mount Ida, is located in this province.

Balıkesir province is famous for its olives, thermal spas, and clean beaches, making it an important tourist destination. The province also hosts immense deposits of kaolinite and borax, with some open-pit mines. The Kaz mountains are also threatened with the expansion of gold mining using cyanide which puts the villagers' lives, the agricultural economy, and tourism at risk.