Thiais (French pronunciation: [tjɛ] ⓘ) is a commune in the southern suburbs of Paris, France.

[3] The name Thiais comes from Medieval Latin Theodasium or Theodaxium, meaning "estate of Theodasius", a Gallo-Roman landowner.

The Austrian writer Joseph Roth, exiled due to his opposition to the Nazi regime, lived at Thiais at the end of the 1930s and is buried at the local cemetery.

Expatriate American journalist and novelist William Gardner Smith died there in 1974.

Thiais is served by Pont de Rungis–Aéroport d'Orly station on Paris RER line C. It is also served by Choisy-le-Roi station on Paris RER line C. This station, although administratively located on the territory of Choisy-le-Roi, lies closer to the town center of Thiais than Pont de Rungis – Aéroport d'Orly station does, and is thus used by people in Thiais.