Abstract: A lithographic apparatus includes an illumination system for providing beam of radiation, and a support structure for supporting a patterning device. The patterning device imparts the beam of radiation with a pattern. The apparatus also includes a substrate table for holding a substrate, a projection system for projecting the patterned beam onto a target portion of the substrate, and a gas supply system for supplying a purge gas including oxygen to a plurality of spaces in the apparatus. The gas supply system is arranged so that the purge gas supplied to each of the plurality of spaces is a premixed purge gas mixture composed by the gas supply system for each of the plurality of spaces on the basis of a predetermined relationship that relates a desired amount of oxygen in the premixed purge gas mixture to the respective space to which that premixed purge gas mixture is supplied.