[en] During irradiation of a solid surface with energetic ions the fate of an implanted ion is determined (1) by its location in the lattice, (2) the defect concentration around the implanted atom, and (3) the mobility of the implanted atom either by thermally activated migration or by interaction with other mobile defects. At low irradiation fluence the fate of the implanted atom is not influenced by interactions with other collision cascades caused by other ions nor with the mobile defects emerging from these cascades. The surface acts as the dominant sink for the defects. At increasingly higher fluences the effects of interference between products of successive collision cascades become visible. Non-linearity in the growth of defect populations is then observed, sometimes including clustering of the implanted atoms. Trapping processes and the early stages of cluster development are discussed for He, the other noble gas atoms, light impurities H and N, and metallic impurities implanted in metals. (Auth.)