During its course, the river collects water from many tributaries and the drainage basin of the Great Zab covers approximately 40,300 square kilometres (15,600 sq mi).

The Zagros Mountains have been occupied since at least the Lower Palaeolithic, and Neanderthal occupation of the Great Zab basin has been testified at the archaeological site of Shanidar Cave.

The Great Zab rises in Turkey in the mountainous region east of Lake Van at an elevation of approximately 3,000 metres (9,800 ft) amsl and joins the Tigris on its left bank in Iraq.

The Great Zab receives most of its waters from the left-bank tributaries; the Rubar-i-Shin, Rukuchuk, Rubar-i-Ruwandiz, Rubat Mawaran and Bastura Chai.

The valleys – including that of the Great Zab – and the south-western foothill zone are filled with gravel, conglomerate, and sandstone; the result of water erosion.

[12][13] The Great Zab rises in the highlands of the Zagros Mountains, where a climate with cold winter and annual precipitation in excess of 1,000 millimetres (39 in) prevails.

[18] In the foothill zone, many areas are now cultivated, but there remain small patches of natural vegetation dominated by herbs of the genus Phlomis.

[25][26] Evidence for human occupation of the Zagros reaches back into the Lower Palaeolithic, as evidenced by the discovery of many cave-sites dating to that period in the Iranian part of the mountain range.

[28][29] A Mousterian stone tool assemblage – produced by either Neanderthals or anatomically modern humans – was recently excavated in Erbil.

[31] M'lefaat on the Khazir River (a tributary to the Great Zab) was a small village of hunter-gatherers dating to the 10th millennium BCE that was contemporary with the Pre-Pottery Neolithic A in the Levant.

[32] An archaeological survey of the Citadel of Erbil, in the plain south of the lower course of the Great Zab, has shown that this site was continuously occupied at least from the 6th millennium BCE upward.

[33][34] The earliest historical reference to the region dates to the Ur III dynasty, when king Shulgi mentioned the city of Urbilum – the ancient name of modern-day Erbil.

[36] This canal ran along the right bank of the Great Zab and cut through a rock bluff by means of a tunnel and is still visible today.

[40] When the Mongols swept over Iraq in the 13th century and sacked Erbil, many survivors sought a refuge in the inaccessible valleys of the Great Zab.