The invention relates to an assembly, preferably for use in a lithography system or a microscopy system, for providing an accurately aligned stack of two or more modules in a stacking direction. Each of the two or more modules comprises three support members. The assembly comprises a frame comprising three planar alignment surfaces which extend in the stacking direction and which are angularly off-set with respect to each other. In addition each of the three support members of each one of the two or more modules, when arranged in said frame, abuts against a corresponding one of the three alignment surfaces. The frame is provided with an opening between two of the three planar alignment surfaces for inserting a module in the assembly, said two planar alignment surfaces on either side of the opening are arranged at least partially facing said opening.