Fish locomotion shows the key features related to swimming. The functional anatomy of relevant parts is described. Species with special swimming skills are discussed. Kinematics of undulations of body and tail and swimming styles using paired and unpaired appendages are described. The wake of a fish shows the interaction between an undulating fish and water. The energy costs of swimming increase with speed. At the optimum speed the amount of work required to cover a unit distance reaches a minimum. Burst-and-coast swimming and schooling are indicated as swimming behaviors with energy-saving potentials. Relationships between swimming speeds and endurance are discussed.