Brétigny-sur-Orge (French pronunciation: [bʁetiɲi syʁ ɔʁʒ] ⓘ, literally Brétigny on Orge) is a commune in the southern suburbs of Paris, France, 26.7 km (16.6 mi) from the city center.

The etymology comes from the Latin britiniacum, which means "property of the Breton".

At the time of the creation of the commune, the city name was spelled without any accent.

The average annual rainfall is 628.9 mm (24.76 in) with December as the wettest month.

It is served by Brétigny station on Paris RER line C. On 12 July 2013 an intercity train derailed shortly after 17.00, killing 7 people.