An illumination optical unit for microlithography illuminates an object field with illumination light. The unit includes a first facet mirror that has a plurality of first facets, and a second facet mirror that has a plurality of second facets. The unit has facet pairs which include respectively a facet of the first facet mirror and a facet of the second facet mirror which predefine a plurality of illumination channels for illuminating the object field. At least some of the illumination channels have in each case an assigned polarization element for predefining an individual polarization state of the illumination light guided in the respective illumination channel.