Photorefractive holograms have received great attention for decades due to their transmissive geometries and dynamic nature. The PR mechanism involves charge generation, charge transport, charge trapping, and modulation of the refractive index. So far, photorefractive hologram is regarded as one of the most important holographic materials with dynamic features. Since the first PR mechanism was described about 50 years ago, extensive investigations have been undertaken by many researchers and it is anticipated that PR materials will be the center of optoelectronic material research in the near future. This article reviews the current understanding of the mechanism responsible for the PR effect and current research trends, and briefly introduces recent progress in applications and material design.