We analyze the interplay between classical and quantum dynamics in ionization of atoms by fast charged particles. The convergence to the classical limit is studied as a function of the momentum transferred to the electron during the collision, the impact parameter, the energy and angle of the emitted electron, and the initial state of the target. One goal is to assess the validity of exact classical (CTMC) methods and approximate classical models such as the Thomson model. Applications to data for electron ejection at large angles are presented. The connection between collisional ionization by charged particles and ionization by half‐cycle pulses is discussed. ©1996 American Institute of Physics.