Seine-et-Oise

thumb|Map of Seine-et-Oise in France, around Seine (department)|Seine thumb|An old Michelin roadsign in Marines, Val-d'Oise|Marines Seine-et-Oise () is a former department of France, which encompassed the western, northern and southern parts of the metropolitan area of Paris. Its prefecture was Versailles and its administrative number was 78. Seine-et-Oise was disbanded in 1968 as part of the reorganisation of the departments of the Paris metropolitan area. The newly created Yvelines department inherited the 78 number.