An illumination system for microlithography is used to illuminate an illumination field by the illumination light of a primary light source. A first grid assembly (12) has bundle-shaped first grid elements (24) that are arranged in a first plane of the illumination system or neighboring the same. The first grid assembly (12) is used to create a grid assembly of secondary light sources. A transmission lens is used for the superimposed transmission of the illumination light of the secondary light sources into the illumination field. The transmission lens has a second grid assembly (15) having bundle-shaped second grid elements (26). Each of the grid elements (24) of the first grid assembly (12) is associated with one of the grid elements (26) of the second grid assembly (15) for guiding a partial bundle (25) of an entire bundle of the illumination light. For example, the first grid assembly (12) has at least two types (I, II, III) of the first grid elements (24), which differ in their bundle-influencing effect. The grid elements (24, 26) of the two grid assemblies (12, 15) are arranged in relation to one another such that every grid element type (I through III) is associated with at least one individual distance (DeltaI, DeltaII, DeltaIII) between the first grid element (24) of said type (I through III) and the associated second grid element (26) of the second grid assembly (15). The result is an illumination system by means of which an influence of specific illumination parameters is possible, if possible without the undesirable influence of other illumination parameters.