An optical element and a lithographic apparatus including the optical element. The optical element includes a first member having a curved optical surface and a heat transfer surface, and a second member that comprises at least one recess, the at least one recess sealed against the heat transfer surface to form at least one closed channel between the first member and the second member to allow fluid to flow therethrough for thermal conditioning of the curved optical surface. In an embodiment, one or more regions of the heat transfer surface exposed to the at least one closed channel are positioned along a curved profile similar to that of the curved optical surface.