In terms of numbers of species, by far the largest family of fish with about 3,000 living and extinct species in about 370 genera. It comprises freshwater fish that typically have a fairly elongate body, a single dorsal fin without true spines, a forked tail fin, ventral fins in the abdominal position, and no teeth on the jaws. Many cyprinidaes are herbivorous, feeding on plants or algae. Most Cyprinids are native to North America, Africa, and Eurasia.

Numerous Cyprinids have become important in the aquarium and fishpond hobbies, known as Koi. Other popular aquarium cyprinidaes include danionins, rasborines, and barb. Most species are now bred in Southeast Asia. One particular species of these small and undemanding danionins is the zebrafish (Danio rerio). It has become the standard model species for studying developmental genetics of vertebrates, in particular fish.