The invention describes an airbag (10) for a vehicle occupant restraint system, wherein the airbag (10) in the inflated state includes a front side (24) forming an occupant impact surface and an opposite rear side (22). The front side (24) and the rear side (22) are formed by shell portions (14, 16) of the airbag (10) being connected to each other at their outer edges (34, 36). The front side (24) is longer along a centerline (M) extending in the longitudinal direction of the airbag (10) than the rear side (22) so that, in the inflated state, the airbag (10) takes a curved shape. The front side (24) has at least one shaping line (42) extending substantially curved and transversely to the centerline (M) at which shaping line two shell portions (34, 36) are connected to each other. The respective outer edges (34, 36) of the front side (24) and the respective outer edges (34, 36) of the rear side (22) are of the same overall length.