A lithographic projection apparatus is disclosed where at least part of a space between a projection system of the apparatus and a substrate is filled with a liquid by a liquid supply system. The projection system is separated into two separate physical parts. With substantially no direct connection between the two parts of the projection system, vibrations induced in a first of the two parts by coupling of forces through the liquid filling the space when the substrate moves relative to the liquid supply system affects substantially only the first part of the projection system and not the other second part.