Professor Josephine Arendt (b 1941) is Emeritus Professor of Endocrinology in the University of Surrey. Trained as a biochemist she is a specialist on biological rhythms and has pioneered the field of chronobiology. She has researched biological rhythms and their mechanisms widely in animals and humans, including studies on jet-lag, sleep disorders in the blind, shift work, and devised techniques to measure melatonin and its metabolites. In this interview and associated material she describes her career and discusses many of these fascinating aspects of her work.