A lithographic method is provided that includes using an illumination system to provide a beam of radiation having an illumination mode, using a patterning device to impart the radiation beam with a pattern in its cross-section, and projecting the patterned radiation beam onto a substrate. The illumination mode is adjusted after the radiation beam has been projected onto the substrate. The adjustment is arranged to reduce the effect of optical aberrations due to lens heating on the projected pattern during projection of the pattern onto a subsequent substrate.