This book presents details of electron impact single ionization of atoms and ions. The ionization of atoms and molecules by photon or charged particle impact such as electrons is of great importance in physics. Over the past several years a great progress has been made to understand the physics of electron impact single ionization processes (i.e. (e, 2e) processes) on atoms and ions and its quantum mechanically complete studies have also been performed. Theoretical investigations of (e, 2e) processes on atoms provide a platform to understand the collision dynamics and the characteristics of the targets by studying triple differential cross section (TDCS). Study of TDCS using the (e, 2e) technique is an important method to probe the dynamics of the ionization process and such data are strongly needed in the fields of astrophysics, controlled nuclear fusion, plasma physics etc. Chapter 1 of this book gives introduction of the electron impact ionization and the details of research work done so far has been described. The theoretical formalism has been described in detail in Chapter 2. Results of TDCS for various atomic and ionic targets have been presented in Chapter 3 and 4.