Guyancourt is a commune situated in the Yvelines department within the Île-de-France region of north-central France. It is located in the south-western suburbs of Paris, approximately 21.2 km (13.2 mi) from the city center.
The commune is part of the "new town" of Saint-Quentin-en-Yvelines. It serves as a residential and urban area within the broader Parisian metropolitan region.