Saint-Ouen (săNtōäˈ) [key], city (1990 pop. 42,611), Seine–Saint-Denis dept., N central France, on the Seine River. It is an industrial suburb N of Paris and a terminal point for river shipping. Electrical equipment, metal products, pharmaceuticals, and perfumes are among the chief manufactures. In 1814, Louis XVIII signed the Declaration of Saint-Ouen, by which he became a constitutional monarch. The city retains a villa from the Merovingian period.