This chapter explores the ways fish swim from zero speeds in station-holding and hovering, through cruising and sprint, to fast starts. The range of power required to swim over such a range is formidable. Effective swimming is achieved by performance range fractionation using gaits. Gaits are defined by the use of various combinations of propulsor type (median and paired fin or body/caudal fin propulsors), propulsor kinematics (station-holding, hovering, steady swimming and fast starts, muscle (red, pink and white), and locomotor behaviour (continuous and burst-and-coast swimming). The number of gaits expressed within lineages, and presumably locomotor performance range, has generally increased over evolutionary time. At any given evolutionary level, radiations have been common, often enhancing certain gaits but reducing performance in others (gait suppression). The range of gaits expressed during ontogeny also increases. Environmental influences tend to reduce metabolic scope so that successive gaits tend to be recruited at lower speeds (gait compression). Directions for future research include use of computational models better to model pressure distributions and forces during swimming. Problems especially of manoeuvrability, agility and stability have been neglected by traditional interest in maximum speed and acceleration.