Electron EM reviews the theoretical and experimental work of the last 30 years on continuous electron emission in energetic ion-atom collisions. High incident energies for which the projectile is faster than the mean orbital velocity of the active electron are considered. Emphasis is placed on the interpretation of ionization mechanisms. They are interpreted in terms of Coulomb centers associated with the projectile and target nuclear fields which strongly interact with the outgoing electron. General properties of the two-center electron emission are analyzed. Particular attention is given to screening effects. A brief overview of multiple ionization processes is also presented. The survey concludes with a complete compilation of experimental studies of ionization cross sections.