La Seyne-sur-Mer, which is part of the agglomeration of Toulon, is situated adjacent to the west of the city.

The population data in the table and graph below refer to the commune of La Seyne-sur-Mer proper, in its geography at the given years.

[3] La Seyne-sur-Mer owed its importance to the shipbuilding trade, the Société des Forges et Chantiers de la Mediterranée having here one of the finest shipbuilding yards in Europe (it is a branch of the larger establishment at Marseille), which gave employment to about 3,000 workers.

The population is diverse in origins and the outer suburbs are undergoing a transformation with old multi storey apartments being replaced with modern developments.

Iraq's "Osiris class" nuclear reactors, later destroyed by Israel in Operation Opera, were built in La Seyne-sur-Mer.