A lithographic projection apparatus includes a substrate table configured to hold a substrate, a projection system arranged to project a patterned beam of radiation onto the substrate, a liquid supply system configured to supply liquid to a space between the projection system and the substrate, and a residual liquid detector configured to detect liquid remaining on the substrate and/or the substrate table after an exposure is completed. A device manufacturing method includes projecting, using a projection system of a lithographic apparatus, a patterned beam of radiation through a liquid onto a substrate, the substrate being held by a substrate table, and, after the projecting is complete, detecting residual liquid on the substrate and/or the substrate table.