Residing within the immense diversity of fishes on earth is an equally impressive array of locomotor abilities. Some fish continuously swim virtually their entire lives; some move primarily in brief bursts of rapid acceleration; some gracefully maneuver through spatially complex habitats; and some even walk on land. What are the evolutionary root causes of such diversity in swimming abilities? Has swimming performance largely been shaped by random factors, evolving at the whim of genetic drift? If not, then what ecological mechanisms might be responsible for the evolution of swimming performance? Here we investigate some of the major ecological factors that might have shaped the evolution of locomotor performance in fishes. Using an integrative approach, we 201acknowledge the complexity of swimming performance, addressing how its evolution depends on numerous underlying organismal features, and is both influenced by and influences multiple fitness components.