Electronic structure of atoms, molecules and solids from (e,2e) studies

The (e,2e) reaction on atoms can be described quite well in most of kinematic space by distorted-wave theories of varying sophistication. In some regions it is necessary to obey the newly-discovered boundary condition for three charged particles. The understanding enables us to recognise a kinematic region where the reaction is sensitive only to the target-ion structure. Single-particle and electron-correlation information has been discovered for a wide range of atoms and molecules. The understanding of solids is developing.