Site attachment, social organization and reproduction traits of the damselfish (Pomacentridae), based on field observations and cytology of gonads, are described. This fish family includes both solitary and gregarious species, as well as species of an intermediate nature. Many of the species are monodomous, using a specific, permanent habitat, whereas others are polydomous, occurring in different habitats or changing their habitat with age. Some of the species are monomorphic, developing their permanent colour when very young, whereas others are polymorphic, demonstrating different colour morphs as juveniles, particularly blue and yellow patterns. The damselfishes include gonochorists, with predetermination of sex, protogynous and protandrous hermaphrodites, and bisexual types in which the gonadal primordi‐um bears both types of gonia. With few exceptions, the polydomous species are primarily gonochorists, and the monodomous ones are hermaphrodites, in which sex determination is socially controlled depending on the type and composition of the surrounding group of conspecifics.