The Shatt al-Arab (Arabic: شط العرب, literally River of the Arabs), or the Arvand Rūd (Persian: اروندرود, literally Arvand River), is a river in Southwest Asia of some 200 km (125 mi) in length, formed by the confluence of the Euphrates and the Tigris in the town of al-Qurnah in the Basra Governorate of southern Iraq. The southern end of the river constitutes the border between Iraq and Iran down to the mouth of the river as it discharges into the Persian Gulf. It varies in width from about 232 m (760 ft) at Basra to 800 m (2 600 ft) at its mouth. It is thought that the waterway formed relatively recently in geologic time, with the Tigris and Euphrates originally emptying into the Persian Gulf via a channel further to the west.

The Karun river, a tributary which joins the waterway from the Iranian side, deposits large amounts of silt into the river; this necessitates continuous dredging to keep it navigable .

The region of Shatt al-Arab is considered to be the largest date palm forest in the world. In the mid-1970s, the region counted some 17–18 million date palms or a fifth of the world's 90 million palm trees. By 2002, more than 14 million, or 80 percent, of the palms were wiped out. In total, war, salt and pests destroyed approximately 14 million palms: around 9 million in Iraq and 5 million in Iran. Moreover, of the remaining 3–4 million palms, many are in poor condition.

In Middle Persian literature and the Shahnama, the name Arvand is used for the Tigris, the confluent of the Shatt al-Arab. Iranians begun using this name specifically to designate the Shatt al-Arab during the later Pahlavi period, and continue to do so after the revolution of 1978-79.