The coherent potential approximation (CPA) is a method, in theoretical physics, of finding the averaged Green's function of an inhomogeneous (or disordered) system. The Green's function obtained via the CPA then describes an effective medium whose scattering properties represent the averaged scattering properties of the disordered system being approximated. It is often described as the 'best' single-site theory for obtaining the averaged Green's function. It is perhaps most famous for its use in describing the physical properties of alloys and disordered magnetic systems, although it is also a useful concept in understanding how sound waves scatter in a material which displays spatial inhomogeneity. The coherent potential approximation was first described by Paul Soven, and its application in the context of calculations of the electronic structure of materials was pioneered by Balász Győrffy.