We give a systematic discussion of the anomalous scattering of Bogoliubov excitations at sharp N–S and S–N boundaries as well as quasi-particle tunneling in N–S–N and S–N–S geometries. The relation between the transmission resonances (E > Δ) and the bound states (E < Δ) in N–S–N and S–N–S geometries is explicitly exhibited. We also work out the extra thermal resistance due to scattering by a normal layer imbedded in a superconductor and by a superconducting layer imbedded in a normal metal, with results different from that obtained by Shikin.