Abstract: The phytochrome molecule is the photoreceptor used by plants to sense environmental red and far-red light changes,which are vital to direct growth and development. In this review, we present (1) the chromoprotein structure of phytochrome, its domains and corresponding functions; (2) members of phytochrome gene families and their evolutionary relationships in the main groups of plants; (3) advances in molecular mechanisms of phytochrome signaling and gene regulation; and (4) prospects for future research.