Damselfish are those within the subfamilies Abudefdufinae, Chrominae, Lepidozyginae, Pomacentrinae, and Stegastinae within the family Pomacentridae. Most species within this group are relatively small, with the largest species being about 30cm in length. Most damselfish species exist only in marine environments, but a few inhabit brackish or fresh water. These fish are found globally in tropical, subtropical, and temperate waters.

Pomacentridae is a family of ray-finned fish, comprising the damselfishes and clownfishes. This family were formerly placed in the order Perciformes but are now regarded as being incertae sedis in the subseries Ovalentaria in the clade Percomorpha. They are primarily marine, while a few species inhabit freshwater and brackish environments. They are noted for their hardy constitutions and territoriality. Many are brightly colored, so they are popular in aquaria.