An illumination system for an EUV projection exposure apparatus is designed for shaping illumination radiation from at least a portion of received EUV radiation. The illumination radiation is directed into an illumination field in an exit plane of the illumination system during exposure operation. An EUV radiation source is arranged in a source module separate from the illumination system. The illumination system includes an alignment state determining system including an alignment detector configured to receive a portion of the EUV radiation emerging from the secondary radiation source and to generate therefrom an alignment detector signal representative of the alignment state.