Myosins are a diverse superfamily of molecular motor proteins, which share the ability to reversibly bind actin and hydrolyse MgATP. They are capable of either translocating actin filaments or translocating vesicles or other cargo on fixed actin filaments. There are currently 15 distinct classes in the myosins superfamily, based on sequence homology. Myosin II and myosin I proteins are familiar and well studied; while Classes III-XV are less well characterized. All myosins examined to date are multimeric and appear to possess at least three functional domains, a head, neck, and tail. Myosins (second edition) explores the structure and functional properties of myosins, their regulation, and mutational analysis. It has been thoroughly updated since the first edition was published in 1995 including sections on the three additional classes defined by new sequences, information provided by the crystal structure of seven new Dicytostelium motor domains, and data from new techniques such as molecular imaging and tagging proteins with GFP 20. The three human diseases that are now known to be linked to mutations in different myosin heavy or light chains are also covered, including more than 50 mutations associated with hyperotrophic cardiomyopathy.