These notes are a result of a series of lectures given to the MS and PhD students of the Department of Physics, Moscow State Pedagogical University. They deal with the subject of electron-phonon interaction in pure three-dimensional metals. The goal was to show how one could calculate the temperature dependence of the electron-phonon-interaction time from first principles within a simple model. Students wishing to expand their knowledge of the subject of condensed matter are invited to study any book on solid-state physics (for example by J.M. Ziman, or N.W. Ashcroft and N.D. Mermin.