This volume summarizes the state-of-the-art methodology for the functional characterization of phytochromes in vitro and in vivo. Chapters and divided into four parts covering, phytochrome discovery, spectroscopic techniques, x-ray crystallography, x-ray crystallography, and analyzing phytochrome function in vitro and in vivo. Written in the highly successful Methods in Molecular Biology series format, chapters include introductions to their respective topics, lists of the necessary materials and reagents, step-by-step, readily reproducible laboratory protocols, and tips on troubleshooting and avoiding known pitfalls. Cutting-edge and comprehensive, Phytochromes: Methods and Protocols aims to be a versatile laboratory bench and computational resource that is an essential reference.