BOULOGNE-BILLANCOURT or BOULOGNE-SUR SEINE (the former title was fixed by decree in 1925), town of northern France, in the department of Seine, on the right bank of the Seine, south-west of Paris and immediately outside the fortifications. Pop. (1931) 85,190. The town has a Gothic church of the 14th and 15th centuries (restored in 1863), founded in honour of Notre-Dame de Boulogne-sur-Mer. The settlement had previously been called Menuls-les-St. Cloud. Laundering is extensively carried on as well as the manufacture of metal boxes, soap, oil and furniture, and there are numerous handsome resi dences. For the neighbouring Bois de Boulogne see PARIS.