Experiments with spin-polarized beams of electrons and/or targets are shown to provide very detailed tests of state-of-the-art theory, particularly if the spin-polarization of the reaction partners and/or the polarization of light emitted after impact excitation is measured as well. Although recent advances in the numerical simulation of electron-atom collisions, based upon the “convergent close-coupling” (CCC) and the “R-matrix with pseudo-states” (RMPS) methods, produce impressive results for light quasi-one and quasi-two electron targets, there are still many open questions left regarding the treatment of more complex systems as well as the interpretation of some of the results. Key examples are presented to illustrate the current status of theory and experiment in the field, followed by suggestions for future developments. ©1999 American Institute of Physics.