Electron collisions with atoms, ions, and molecules have been investigated since the earliest years of the last century because of their pervasiveness and importance in fields ranging from astrophysics and plasma physics to atmospheric and condensed matter physics. Written in an accessible yet rigorous style, this book introduces the theory of electron-atom scattering into both the non-relativistic and relativistic quantum frameworks. The book also includes exercises with an increasing degree of difficulty to allow the reader to become familiar with the subject.