An illumination optical unit for EUV projection lithography serves for guiding illumination light towards an illumination field, in which a lithography mask can be arranged. The illumination optical unit has a first facet mirror having a plurality of individual mirrors. The latter predefine illumination channels for guiding illumination light partial beams towards the illumination field. A second facet mirror of the illumination optical unit is disposed downstream of the first facet mirror and has a plurality of facets. The latter respectively contribute to the imaging of a group of the individual mirrors of the first facet mirror into the object field via a group-mirror illumination channel. The latter comprises the individual-mirror illumination channels of the individual-mirror group. Images of the different individual-mirror groups are superimposed on one another in the object field via the assigned group-mirror illumination channels.