This is a volume under Springer Solid State Science. The Point-Contact Spectroscopy (PCS), was designed for study of the conduction-electron interaction mechanism with a whole class of elementary excitations in the solids. In PCS, a small constriction, about a few nanometers large, between two conductors plays a role of a spectrome ter. Namely, because of inelastic scattering of accelerated electrons, the I - V characteristic of such a tiny metallic contact is nonlinear versus an applied voltage and its second derivative surprisingly turns out to be proportional to the electron-quasiparticle-interaction spectrum.