Similarities and differences in mating, birth and parenting within a broad sample of nocturnal species from four prosimian families are addressed in this issue. Most of the papers were part of a symposium held at the 19th International Primatological Society Meeting in Beijing, China, in 2002. Parental care and mating systems are more complex than previously thought. While males in some species (Cheirogaleus medius) are regularly cuckolded, in others (Microcebus murinus) the dominant males obtain nearly all the matings and fertilisations. While some species regularly cache and carry their young throughout the night, others park them throughout the night. It is hoped as more of these studies are undertaken that it will be possible to perceive common features and differences among nocturnal species and by so doing to illuminate the underlying evolutionary processes leading to their diverse social patterns. This theme issue will be of special interest to primatologists.