A vehicle seat can be produced economically in various sizes and fitted out in various ways suitable for any application by virtue of construction utilizing extruded profiles. A seat module with continuous seating-surface and back-rest segments in a variety of widths is provided. The seat module is self-supporting over the whole width of the seating surface and is made up of two or more hollow shaped-section members running parallel to the front edge of the seating surface. These hollow members have adequate stiffening features in the form of webs and other reinforcements and are partly or completely attached to each other by frictionally locking structure or by the fact that they are integrally jointed to each other. The open sides of the seat module are closed off by coverings and the module supported at one or both sides. Other embodiments are directed to connection of arms and head rests, and the way in which the upholstery is attached.