Guyancourt (pronounced: [ɡɥi.jɑ̃.kuʁ]) is a commune in the Yvelines department in the Île-de-France region in north-central France. It is located in the south-western suburbs of Paris 21.2 km (13.2 mi) from the center, in the "new town" of Saint-Quentin-en-Yvelines.