Ionization of atoms by electron impact

Ionization of atoms by electrons is one of the most common atomic scattering processes. We review the progress in modeling the ionization process from early quantum models in the 1920s to the present day. Despite the fact that ionization is so fundamental, the path to precision calculations even for the simplest systems has been slow and tortuous. In the past decade major progress has been achieved with the aid of new methods and rapid increase in computing power and we illustrate some of the important developments by focusing on total ionization cross-sections.