Paris-Sud University, also known as the University of Paris — XI, was a French research university distributed among several campuses in the southern suburbs of Paris, including Orsay, Cachan, Châtenay-Malabry, Sceaux, and Kremlin-Bicêtre campuses. In 2020, the university was replaced by the Paris-Saclay University.

Orsay is a commune in the Essonne department in Île-de-France in northern France. It is located in the southwestern suburbs of Paris, France, 20.7 km (12.9 mi) from the centre of Paris.