The Bosna (, ) is the third longest river in Bosnia and Herzegovina, and is considered one of the country's three major internal rivers, along with the Neretva and the Vrbas. The other three major rivers of Bosnia and Herzegovina are the Una, to the northwest; the Sava, to the north, and the Drina, to the east. The river is thought to be the namesake of Bosnia. The river Bosna flows for .
The river is possibly mentioned for the first time during the 1st century AD by Roman historian Marcus Velleius Paterculus under the name Bathinus flumen. Another basic source that is associated with the hydronym Bathinus is the Salonitan inscription of the governor of Dalmatia, Publius Cornelius Dolabella, where it is said that the Bathinum river divides the Breuci from the Osseriates. Another name could also have been Basante.
According to philologist Anton Mayer, the name Bosna could be derived from Illyrian Bass-an-as(-ÃÂ), which would be a diversion of the Proto-Indo-European root ', meaning 'the running water'.
The Bosna River has created the Bosna River Valley. The valley has been developed as the country's industrial hub and is home to nearly a million people, who live primarily in several major cities.
The Bosna source is the Vrelo Bosne spring, located at a.s.l. (according to an earlier source, a.s.l.) at the foothills of mount Igman, on the outskirts of Sarajevo, capital of Bosnia and Herzegovina. The spring is one of Bosnia and Herzegovina's chief natural landmarks and tourist attractions.
The course between the source and its largest tributary in this section, the à ½eljeznica, which runs in from the right, is referred as the Mala Bosna (), but the section is often extended all the way to its confluence with Miljacka, four kilometers downstream. Its tributaries between the source and the à ½eljeznica are first the VeÃÂerica and then Bukulaà ¡, while in the region of extended Mala Bosna course it further receives, first the à ½eljeznica from the right, then approx. 600 meters downstream the Zujevina, the only tributary from the left in this region, followed by the Dobrinja (a.k.a. Tilava) 1.5 km, and then 2 km further the Miljacka, both from the right.
The Upper Bosna is a section between its source and the mouth of the Laà ¡va, a left tributary, just upstream from Zenica. The section encompasses the entire region between Ilidà ¾a, near Sarajevo, and the Laà ¡va, including the spacious valley between Ilijaà ¡ and Kakanj. The Visoko region, with its medieval heritage, is at the center of this area.
The Middle Bosna is mostly composed of gorges, with steep slopes and narrow passages, between Zenica and Doboj. In this section, there are several medieval sites, such as Vranduk, Maglaj and Doboj.
The Lower Bosna is the last section of the Bosna. From Doboj, the river continues northwards, approaching the Sava through the heart of Bosnia, passing through the lowlands of Posavina, and eventually becomes a right tributary of the Sava in Bosanski à  amac. There, it empties at around above the sea level.
The Bosna flows through a number of cantons. From its starting point in the Sarajevo Canton, it flows through the Zenica-Doboj Canton, and the Posavina Canton, in that order. On its way north, the Bosna also passes through the cities of Visoko, Zenica, Maglaj, Doboj, ModriÃÂa and Bosanski à  amac.
The main right tributaries are: à ½eljeznica, Miljacka, Ljubina, MisoÃÂa, Stavnja, Trstionica, Zgoà ¡ÃÂa, , Krivaja and SpreÃÂa. On the left, the main tributaries are: Zujevina, Fojnica, Laà ¡va and Usora.