The invention relates to a lithographic projection assembly, having at least two load locks for transferring substrates between a first environment and a lower pressure second environment, a substrate handler with a handler chamber within the second environment and a lithographic projection apparatus including a projection chamber. The handler chamber and the projection chamber communicate via a load position for entering a substrate from the handler chanter into the projection chamber and an unload position for removing the substrate from the projection chamber into the handler chamber. The handler chamber also includes pre-processing means for pre-processing of the substrates and transport means for transferring substrates between the load locks and pre-processing means.