Peak performances in sport require the full deployment of all the powers an athlete possesses. How factors such as mechanical power output, technique and drag, each individually, but also in concert, determine swimming performance is the subject of this enquiry. This overview of swimming biomechanics focuses on three performance factors: (i) generation of propulsion in water; (ii) drag encountered by the body during swimming; and (iii) propulsive efficiency. Theoretical considerations will be put to use by predicting individual power requirements for swimming a world record in the 50 m freestyle based on experimental data. © Koninklijke Brill NV, Leiden 2005.