Molecular motors lie at the heart of biological processes from DNA replication to vesicle transport. Our laboratory seeks to understand the physical mechanisms by which these nanoscale machines convert chemical energy into mechanical work. We use single molecule tracking and manipulation techniques to observe and perturb substeps in the mechanochemical cycles of individual motors. Protein engineering helps us to explore relationships between molecular structures and mechanical functions. Broad topics of current interest include torque generation by DNA-associated ATPases and mechanical adaptations of unconventional myosins.