Abstract: A method for heating an optical element in an optical system, such as in a microlithographic projection exposure system comprises using a thermal manipulator to introduce a heating power into the optical element to produce a thermally induced deformation. Before starting operation of the optical system in which useful light impinges on the optical element, the heating power is adjusted with respect to a desired state of the optical element in which a first optical aberration is at least partially compensated. After starting operation of the optical system, the heating power is regulated to the desired state depending on the heat load of the useful light impinging on the optical element. The heating power is regulated in such a way that the average temperature of the optical element remains constant up to a maximum deviation of 0.5 K.