The present invention relates to a gas generator, in particular for airbag modules in motor vehicles, comprising two generator stages each of which includes in its pressure housing at least one igniter, at least one propellant charge and at least one combustion chamber. An inner generator stage is arranged at least substantially inside an outer generator stage and the two generator stages are arranged at least partly in a common filter housing together with a common filter unit arranged outside a pressure housing of the outer generator stage.