The ability to convert a high quality single crystal superlattice structure into a high quality single crystal uniform alloy is a very important technological process. The phenomenon of impurity induced disordering (IID), by which the introduction of some impurity into the crystal lattice enhances the interdiffusion of the lattice constituent species, has been shown to be capable of achieving this homogenization of periodic structures. IID, first observed in 1980 by diffusion of zinc into AIGaAs superlattices, has received a great deal of attention in recent years. Many different impurities have proven capable of enhancing the rate of layer interdiffusion. Because of the complex interactions among the impurities and the atomic lattice, the magnitude of the increase in the lattice interdiffusion coefficient has been shown to depend strongly on the impurity species and the constituent compositions of the layers. Impurity induced disordering has been observed with impurities introduced in three different ways: diffusion from the surface, ion implantation, and doping during epitaxial growth. Selective disordering has been achieved by patterning this source, e.g., with a photolithographic mask or modulated-focused ion beam or by laser scanning. State-of-the-art index-guided lasers and lasers with non-absorbing facets have already been demonstrated using either Zn or Si as the impurity. It seems very likely that the process of impurity induced disordering will play a key role in the future of optoelectronic devices.