The Iraqi–Syrian border runs for a total length of 599 km (372 mi) across Upper Mesopotamia and the Syrian desert. It was first defined in the 1920–23 Paulet–Newcombe Agreement, as an amendment to what had been designated the A zone in the Sykes–Picot Agreement of 1916. In 1932, it was finalised following a League of Nations commission review.
The border passes across Upper Mesopotamia, beginning at the Iraqi–Syrian–Turkish tripoint on the Tigris river at . The border more or less follows the former border between the Mosul and Diyarbekir vilayets of the Ottoman Empire.
From the Euphrates, the border cuts across the part of the Syrian desert (the former Zor sanjak) to the Iraqi–Syrian–Jordanian tripoint at . The border crossing between Al Waleed in Iraq and Al Tanf in Syria is a short distance north-east of the tripoint, and there are Palestinian refugee camps on both sides, the Al-Waleed camp and the Al Tanf camp.
During the Syrian Civil War and Iraqi Civil War, at its height, much of the border fell under the control of the Islamic State of Iraq and the Levant (ISIL), although its northernmost portion remains under Kurdish control, forming the border between Rojava and Iraqi Kurdistan. The Semalka border crossing is a pontoon bridge across the Tigris established by the Kurdistan Regional Government during the Syrian Civil War about 1 km (0.62 mi) downstream from the Iraqi–Syrian–Turkish tripoint, and just north of Faysh Khabur in Iraq.
- CIA Factbook
- International Boundary Study, No. 100 – May 15, 1970, Iraq – Syria Boundary: "The boundary as it is today is based on the League of Nations Report of the Commission entrusted by the Council with the study of the Frontier between Syria and Iraq, Geneva, September 10, 1932."