Doboj (Serbian Cyrillic: Добој) is a city and a municipality in northern Bosnia and Herzegovina, situated in the northern part of the Republika Srpska entity on the river Bosna. Doboj is the largest national railway junction; as such, the seats of the Republika Srpska Railways, and the Railways Corporation of Bosnia and Herzegovina are located in Doboj. It is one of the oldest cities in the country and one of the most important urban centers in Northern Bosnia and Herzegovina.

The first official mention of the settlement is from 1415, as it was written in the charter issued by Dubrovnik to Holy Roman Emperor Sigismund, although there are numerous artefacts and objects that have been found (The National Museum of Bosnia/Herzegovina in Sarajevo & The Regional Museum in Doboj) and which confirm the fact that the area had been inhabited ever since the early stone age, and that the Roman Empire had an army camp (Castrum) and a settlement (Canabea) in the vicinity of the town dating from the 1st century AD. Following the arrival of the Slavs in the 6th century it became a part of the region/bannate Usora (in the medieval documents sometimes put together with the nearby province Soli, hence, Usora and Soli).