An Illumination system for a microlithographic projection exposure apparatus has a light source and a first optical raster element that is positioned in or in close proximity to a first plane. The first plane is conjugated to a pupil plane of the illumination system by Fourier transformation. A second optical raster element is positioned in or in close proximity to the pupil plane. A third optical raster element is positioned in or in close proximity to a second plane that is also conjugated to the pupil plane by Fourier transformation. The third optical raster element, which can be a diffractive optical element, introduces an additional degree of design freedom for the modification of the angular distribution of the projection light bundle.