An understanding of the collisions between micro-particles is of great importance for the number of fields belonging to physics, chemistry, astrophysics, biophysics and so forth. In this work a theory for electron-atom and molecule collisions is developed using non-relativistic quantum mechanics in a systematic manner. The scattering theory is an essential part of the quantum mechanics course of all universities. During the last 30 years, the author has lectured on the topics presented in this book (collisions physics, photon-atom collisions, electron-atom and electron-molecule collisions, "electron-photon delayed coincidence technique"etc.)