Bohinj (Slovene pronunciation: [ˈbɔ̀ːxin]; German: Wochein), or the Bohinj Valley (Slovene: Bohinjska dolina) or Bohinj Basin (Slovene: Bohinjska kotlina), is a 20 km long and 5 km wide basin in the Julian Alps, in the Upper Carniola region of northwestern Slovenia. It is traversed by the Sava Bohinjka river. Its main feature is the periglacial Lake Bohinj (Slovene: Bohinjsko jezero). Bohinj is part of the Municipality of Bohinj, the seat of which is Bohinjska Bistrica.

The basin consists of four geographic units: the Lower Valley (Slovene: Spodnja dolina), Upper Valley (Zgornja dolina), Ukanc Basin or Lake Basin (Ukanška kotlina; Jezerska kotlina), and Nomenj Basin (Nomenjska kotlina). It is bounded by the Komarča head wall on one end and Soteska Canyon at the other. The Lower Bohinj Mountain Range represents its southern border. The Sava River has carved a canyon between the Jelovica and Pokljuka plateaus in the east. To the north, Mount Triglav, Slovenia's highest mountain, is also a part of the municipality.

The Sava Bohinjka (which merges with the Sava Dolinka into the Sava) begins when two rivers, the Jezernica and the Mostnica, merge. The Mostnica comes from the Voje Valley, whereas the Jezernica is a very short river that flows from Lake Bohinj. Many smaller streams flow into the lake. The largest of them, the Savica, emerges in Komarča as a large waterfall. Savica Falls (Slap Savica) gets most of its water from Black Lake (Črno jezero), which is the largest in the Triglav Lakes Valley (Dolina Triglavskih jezer).

The name Bohinj originally applied to the village of Srednja Vas v Bohinju and was attested as such in written sources in 1065 as Bochingun (and as Bochingin in 1085–90, and Uochina in 1120). As a regional name, it appears in written sources in 1250 as Vochina (and as Fochin in 1253, Vochino in 1287, and Bochino in 1333). The name is derived from *Boxyn'ь, which is of unclear origin. One possibility is that it is derived from the hypocorism *Boxъ. Suggestions that it is of Celtic substratum origin are unlikely.

A popular pseudoetymology of the name is the following story: God was giving land to people and, as he finished, he realized that he had forgotten about a small group of people, who were silent and did not insist like the others. Because of their modesty and patience, he felt pity for them. That is why he decided to give them the most beautiful land of all, which he had set aside for himself. It is called Bohinj, because we call God Boh.

The basin is often referred to as a valley due to lack of a clear distinction between a valley and a basin. Another reason may be that the Slovene word dolina 'valley' in the names of various Slovenian regions does not refer to a valley in the geomorphological sense, but in the sense of an area at a lower elevation surrounded by higher land, which is a much more common understanding of the term.

Geographic circumstances have contributed to isolation of Bohinj in the past. The 5,000 inhabitants are mostly descendants of the native people of Bohinj. There are historical findings that prove the valley was populated as early as in the Bronze Age.

France Prešeren, Slovenia's leading poet, wrote the epic-lyric poem The Baptism on the Savica, which is largely fictional but depicts the time of violent baptism of pagans and battles between the Christians and pagans. Most of the story takes place in Bohinj and in Bled.