Doboj is a city in Republika Srpska, Bosnia and Herzegovina. It is situated on the banks of the Bosna river, in the northern region of Republika Srpska. As of 2013, it has a population of 71,441 inhabitants. Doboj is the largest national railway junction and the operational base of the Railways Corporation of Bosnia and Herzegovina. It is one of the oldest cities in Bosnia and Herzegovina and, aside from Banja Luka, the most important urban center in northern Republika Srpska.