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Collisions involving electrons, photons, and atomic systems are important in upper atmospheric and astrophysical phenomena and in the exploration of space. Some of these types of reactions are enumerated and described. Examples are given of their significance with respect to diffusion in the atmosphere; radio communications and radar tracking; the excitation and study of the airglow and aurorae; the Van Allen radiation belts; estimation of densities, composition, and temperatures of nebulae and stellar atmospheres; the mapping of hydrogen in interstellar space; and the erosion of space vehicles and planets. Some of the work at the Georgia Institute of Technology on ion mobilities, ion-molecule reactions, ionization, and charge transfer is described.