Theoretical work dealing with the electron-phonon interaction (EPI) and its effects on the physical properties of metals is reviewed. The many-body approach and that using Landau’s Fermi-liquid theory are briefly described and their adequacy is demonstrated for low values of the adiabaticity parameter (ω_D/ε_F)^(1/2), where ω_D is the characteristic photon frequency, and ε_F is the Fermi energy. Density functional theory is applied to EPI calculations are outlined, and for a number of simple and transition metals, the results of calculations for EPI spectral densities and EPI-dependent physical properties are presented. The potentialities and the range of validity for EPI applications of the density functional method are discussed.