The Communauté d'agglomération Saint Germain Boucles de Seine is the "communauté d'agglomération", an intercommunal structure, in the western suburbs of Paris. It is located in the Yvelines and Val-d'Oise departments, in the Île-de-France region, northern France. It was created in January 2016. Its population was 330,097 in 2016. Its seat is in Le Pecq.