A lithographic apparatus is disclosed. The apparatus includes a support constructed to support a patterning device, the patterning device being capable of imparting a radiation beam with a pattern in its cross-section to form a patterned radiation beam. A projection system is configured to project the patterned radiation beam onto a target portion of a substrate. A first vacuum environment contains the projection system, a second vacuum environment contains the patterning device support, and a separator separates the first and second vacuum environments. The separator includes an aperture for passing the projection beam from the first vacuum environment towards the patterning device and/or vice-versa. The patterning device forms at least part of a seal for substantially sealing the aperture of the separator.