An apparatus and method for controlling temperature of a patterning device in a lithographic apparatus, by flowing gas across the patterning device. A patterning apparatus includes: a patterning device support structure configured to support a patterning device; a patterning device conditioning system including a first gas outlet configured to provide a gas flow over a surface of the patterning device and a second gas outlet configured to provide a gas flow over a part of a surface of the patterning device support structure not supporting the patterning device; and a control system configured to separately control the temperature of the gas exiting the first and second gas outlets such that the gas exiting the second gas outlet is at a higher temperature than the gas exiting the first gas outlet and/or to separately control the temperature and gas flow rate of the gas exiting the first and second gas outlets.