A lithographic apparatus includes a projection system configured to project a patterned radiation beam onto a target portion of a substrate. The projection system has a final element. The apparatus also includes a barrier member surrounding a space between the projection system and, in use, the substrate, to define in part with the final element a reservoir for liquid. The barrier member is spaced from the final element to define a gap therebetween. The apparatus further includes a deformable seal between a radially outer surface of the final element and a radially outer surface of the barrier member. The deformable seal is configured to substantially prevent a gas from flowing past the seal towards or away from the reservoir of liquid.