Recent experimental advances in structural biology, biophysics, and molecular biology have dramatically increased our understanding of the molecular mechanism of muscle contraction, as well as the assembly of myosin filaments. Future studies are required to detail, for example, the molecular cause of the conformational change during the power stroke and ATP hydrolysis, as well as the nature of the communication between nucleotide and actin binding sites. Based on the structural and functional homology between myosin and other molecular motors, these findings have implications not only for understanding muscle contraction, but for understanding numerous aspects of motility in all cellular systems as well.