Single and multiple ionization of atoms by electron impact

We report progress achieved during decades on direct single and multiple io nization of simple atoms by electron collsion. In particular we investigate total cross sections from threshold to high energies. We show that all exp erimental data compare favorably with Wannier threshold theory. A better un derstanding of the ionization process one gets from the analysis of multipl y differential cross sections. To this end we discuss (e, 2e) and (e, 3e) e vents.