Hindu Kush, major mountain system, central Asia, extending generally in a southwesterly direction for 1,000 km (600 mi), from the mountainous region of the Pamirs on the borders of Afghanistan; North-West Frontier Province, Pakistan; and Tajikistan. The system lies largely in northeastern Afghanistan. Outlying ranges, principally the Paropamisus and the Safed Koh, extend the Hindu Kush system across Afghanistan almost to the Iranian border. These mountains, consisting of granites and schists, or crystalline rocks, were probably uplifted in the Tertiary period. The system is in part marked by overthrust of Cretaceous limestones on Cenozoic shales and clays.

In the first 160-km (100 mi) section west of the Pamirs, the Hindu Kush extends southward. In this section the system has a comparatively wide, plateaulike summit, dotted with small glacial lakes, and passes ranging in height from 3,800 to 5,300 m (12,500 to 17,500 ft) above sea level. The system then turns to the southwest and gains in elevation, and the plateau summit breaks into peaks, the highest of which is Tirich Mīr, 7,690 m (25,230 ft) above sea level, in Pakistan. Many other peaks in this section rise more than 6,100 m (20,000 ft), and the system is broken by such passes as the Baroghil, the Dorāh, and the Khāvāk. The Hindu Kush is also the source of many rivers; the most notable are the Amu Darya River on the northern slopes and the Helmand, Kābul, and Konar Rivers and several tributaries of the Indus River on the southern slopes.