In addition to the accumulation of the implanted species, a considerable number of processes can affect the composition of an alloy in the surface region during ion bombardment. Collisions of energetic ions with atoms of the alloy induce local rearrangement of atoms by displacements, replacement sequences and by spontaneous migration and recombination of defects within cascades. Point defects form clusters, voids, dislocation loops and networks. Preferential sputtering of elements changes the composition of the surface. At temperatures sufficient for thermal migration of point defects, radiation-enhanced diffusion promotes alloy component redistribution within and beyond the damage layer. Fluxes of interstitials and vacancies toward the surface and into the interior of the target induces fluxes of alloying elements leading to depthdependent compositional changes. Moreover, Gibbsian surface segregation may affect the preferential loss of alloy components by sputtering when the kinetics of equilibration of the surface composition becomes competitive with the sputtering rate. Temperature, time, current density and ion energy can be used to influence the individual processes contributing to compositional changes and, thus, produce a rich variety of composition profiles near surfaces.