Odžak is a town and municipality located in Posavina Canton of the Federation of Bosnia and Herzegovina, an entity of Bosnia and Herzegovina. It is situated in the northern part of Bosnia and Herzegovina, near the river Sava, 10 km (6.2 mi) from the border with Croatia. The name is derived from Turkish Ocak, during its time as a frontier town of the Ottoman Empire, and means "fireplace" in Turkish and "chimney" in modern Bosnian.

The Posavina Canton is one of ten cantons of the Federation of Bosnia and Herzegovina in Bosnia and Herzegovina. It is the smallest canton with an area of only 330.85 km2 (128 sq mi). The canton is an exclave of Federation of Bosnia and Herzegovina, being bordered by Republika Srpska and Brčko District to the south and the river Sava and Croatia to the north. Its capital is Orašje and the largest town is Odžak.