Magnetic impurities generally have a tendency to lower the superconducting transition temperature, because the antiparallel spin correlations in the superconducting state prevents the valence electron-magnetic ion interaction from entering as favorably as in the normal state. There is a large body of literature dealing with the effect of magnetic and nonmagnetic impurities on the properties of superconductors. A related problem is the structure of the superconductor normal-metal phase boundary. In addition there are many interesting problems associated with superimposed films of normal and superconducting metals. It is well known that a superconductor can make a nearby normal metal become superconducting by allowing the electrons of the two metals to intermingle. Although the effect of the pairing correlations in nuclei is not as striking as in superconductors, it is clear that these correlations play an important role in determining the properties of nuclei.