During the past few years, there have been exciting developments in the field of flavoenzymology. New flavoenzymes have been discovered that are implicated in a variety of biological processes, including cell signaling, chromatin remodeling and cell development. The structures of several of these new flavoenzymes have been described, as exemplified by crystallographic analyses of MICAL, histone demethylase LSD1 and tryptophan dehalogenase. In addition, new structural information has revealed the evolutionary and mechanistic complexity of the enzymes of the riboflavin biosynthetic pathway. The integration of the enzymology data with crystallographic studies at atomic resolution is resulting in unprecedented insight into the chemical and geometric properties underlying flavoenzyme function.