Molecular motors convert chemical energy into mechanical work and provide the engine for all motion in the body, from beating of the heart to division of cells. The myosin family of motor proteins consists of seventeen members, which are involved in a wide variety of cell movements and changes in cell shape. Cytokinesis, directed cell migration, morphogenetic changes in cell shape, and muscle contraction involve myosin II. Myosin V, on the other hand, drives vesicular movement in neurons, melanocytes, and other cells. Due to the unusual features of myosin V (especially its processivity and its large step size), more detail regarding the coupling of the nucleotide state of the protein and its conformation is available than for any other motor protein. However, fundamental questions regarding the basic function of this molecular machine remain unanswered. How do the “legs” of the myosin molecule advance? What are the relative contributions of conformational change, elastic energy, and diffusion to the motion? How does the structure of myosin V facilitate its function? Our work is addressing these questions.