We review the applications of ion implantation in several III-V materials, and rapid thermal annealing techniques to activate the implant and remove the crystalline damage. Ion implantation has become the preferred technique when selective area doping is necessary. It has been used successfully to fabricate n, n+, p, p+, and semi-insulating regions in III-V binary, ternary, and quaternary compounds, and multilayer structures. Ion implantation has also been used to produce layer mixing in multilayer structures, and superlattice disordering. The annealing step necessary to activate the implant and remove the crystalline damage is complicated by several factors such as incongruent evaporation of the group V element, layer mixing, and dopant redistribution. Rapid thermal annealing techniques, which typically employ anneal times between 1 second and 100 seconds, are generally more suitable than conventional furnace annealing. The short annealing times result in much less dopant redistribution, and reduced layer mixing in multilayer structures. Even for short annealing times, it is necessary to employ a protection scheme to suppress the loss of the group V element. Several such methods are discussed, including dielectric encapsulation, proximity techniques, and controlled ambient techniques.