After a brief historical introduction about photorefractive materials, this chapter provides an extensive overview of the mathematical modeling of the photorefractive effect in organic compounds. The theories of charge photogeneration, transport and trapping, as well as chromophore orientation in the space-charge field are detailed. We then discuss the different molecular species providing the respective functionalities to the PR effect: electroconductive matrices, nonlinear chromophores, photo-sensitizers, and plasticizers, along with the recent developments in the search for more effective materials. Several electrode geometries for different types of devices are described before a section on material characterization. This later include measurement techniques of the molecular properties such as energy levels, photoconduction, and index change, followed by the holographic setups such as four-wave mixing and two-beam coupling, along with the theory to extract the important parameters out of the measured quantities.