Tešanj is a town and municipality in the northern part of Bosnia and Herzegovina, located near Teslić, Doboj and Zavidovići. Administrativley, it belongs to the Zenica-Doboj Canton of the Federation of Bosnia and Herzegovina.

Tešanj is located on an altitude of 230 meters and developed around the river Tešanjka.

The present name of the city is for the first time mentioned in 1461 in a charter from King Stephen Tomašević to his uncle Radivoj Krstić. The charter stated that King Stephen Tomašević grants him, among other possessions "i na Usori grad Tešanj- the city of Tešanj, in the Usora region".

Between the second half of the 15th century and the first half of the 16th century, the history of Tešanj was rather chaotic. Since Bosnia was considered a buffer state by the Ottomans, it changed rulers quite often, alternating between Ottoman and Hungarian occupation. Between 1463 and 1476 Tešanj was the center of the Bosnian kingdom and the residence of Duke Radivoj Kotromanić.

From 1512 (or 1520-21) on, Tešanj was under continuous rule of the Ottoman empire. The most Ottoman influential ruler of Tešanj was the Bosnian Sandžak-bey Gazi Ferhad-bey. It is under his authority that the city rapidly developed. His most significant contribution was the Ferhadija Mosque (1563), which still stands in the old town, dating back to the 16th century. Gazi Ferhad-bey died in 1568 and was buried in the yard of the mosque. The epitaph on his tombstone was in Arabic, and is the oldest Islamic record in Tešanj.