The (Urdu: سندھ Sindh; Sindhi: سنڌو Sindh; Sanskrit and Hindi: सिन्धु ; Persian: Hinduحندو ; Pashto: Abasin ّآباسن""; Tibetan: Sengge Chu ""; Chinese: 印度 Yìndù; Greek: Ινδός Indos) is the longest and most important river in Pakistan and one of the most important rivers on the Indian subcontinent. The name "India" is a reference to the Indus River. Originating in the Tibetan plateau in the vicinity of Lake Mansarovar, the river runs a 3200 kilometer (2000 mile) course, through Ladakh district in Kashmir and Northern Areas, flowing through the North in a southerly direction along the entire length of country, and merges into the Arabian Sea near Pakistan's port city Karachi.

The river's estimated annual flow stands at around 207 cubic kilometers. Originating with water from snow and melting glaciers, the river supports an ecosystem of temperate forests, plains and arid countryside. The major cities of the Indus Valley Civilization (IVC), Harappa and Mohenjo Daro, dating to around 3300 B.C.E., represent some of the largest human habitations of the ancient world. Most scholars believe that settlements of Gandhara grave culture of the early Indo-Aryans flourished in Gandhara from 1700 to 600 B.C.E.

The Indus was crossed by the retreating armies of Alexander the Great, and by the Muslim armies of Muhammad bin Qasim, Mahmud of Ghazni and Babur, who crossed the river to strike into the inner regions of Gujarat, Punjab, and Rajputana. The Indus plains were also under the domination of the Persian Empire and the Kushan Empire. The Indus River provides vital water resources for the economy of Pakistan, especially for the breadbasket of Punjab province, which accounts for most of the nation's agricultural production, and Sindh. Access to the waters of the Indus has been a subject of contention between India and Pakistan, who signed the Indus Waters Treaty in 1960.