A lithographic projection apparatus includes an illumination system that conditions a radiation beam, a support structure that holds a patterning device, the patterning device being capable of imparting the radiation beam with a pattern, a substrate table that holds a substrate, and a projection system that projects the patterned radiation beam onto a target portion of the substrate. In addition, a liquid supply system provides a liquid to a space between the projection system and the substrate, the liquid supply system having a member. A liquid seal device forms a liquid seal between the member and the substrate.