An (e,2e) experiment is the measurement of an electron impact ionization process where both the exiting electrons are detected in coincidence. Such measurements are almost at the limit of what can be known, in quantum mechanical terms, and its description presents a substantial theoretical challenge. There are at least two very good reasons for studying (e,2e) and related processes. In the first place we are now only beginning to understand the dynamics of the collision process. The range and sophistication of present experiments allow us to identify kinematic regimes where delicate and...