We review what we have learned about the scattering of electrons by the interfaces between two different metals (M1/M2) in the current-perpendicular-to-plane (CPP) geometry. In this geometry, the intrinsic quantity is the specific resistance, AR, the product of the area through which the CPP current flows times the CPP resistance. We describe results for both non-magnetic/non-magnetic (N1/N2) and ferromagnetic/non-magnetic (F/N) pairs. We focus especially upon cases where M1/M2 are lattice matched (i.e., have the same crystal structure and the same lattice parameters to within similar to 1%), because in these cases no-free-parameter calculations of 2AR agree surprisingly well with measured values. But we also list and briefly discuss cases where M1/M2 are not lattice matched, either having different crystal structures, or lattice parameters that differ by several percent. The published calculations of 2AR in these latter cases do not agree so well with measured values. (C) 2009 Elsevier B. V. All rights reserved.