The term rex rabbit refers informally to one of at least eight breeds of domestic rabbit. One such breed is the Rex, which is recognized by the American Rabbit Breeders Association (ARBA) and by the British Rabbit Council (BRC). Other modern-day rex rabbit breeds are listed below. Care must be taken to distinguish the rex rabbit breeds from the three types of rex rabbit fur for which they are known.

The rex mutation is a genetic variation in mammals that results in soft curly fur. These effects are due to changes in the structure of groups of hairs and cross-section of individual hairs. The rexed coats are unusual but occur in cats, rats, rabbits, horses, and dogs. The mutations, infrequent and spontaneous, occur in a variety of genes and genetic regulatory structures. The diversity of genetic factors results in variable coat thickness/density and fur length. A similar mutation can affect the feathers of birds.