Canine distemper (CDV) (sometimes termed "footpad disease") is a viral disease that affects a wide variety of mammal families, including domestic and wild species of dogs, coyotes, foxes, pandas, wolves, ferrets, skunks, raccoons, and felines, as well as pinnipeds, some primates, and a variety of other species. CDV does not affect humans.

In canines, CDV affects several body systems, including the gastrointestinal and respiratory tracts, the spinal cord, and the brain. Common symptoms include high fever, eye inflammation and eye/nose discharge, labored breathing and coughing, vomiting and diarrhea, loss of appetite and lethargy, and hardening of the nose and footpads. The viral infection can be accompanied by secondary bacterial infections and can eventually present serious neurological symptoms.

Canine distemper is caused by a single-stranded RNA virus of the family Paramyxoviridae (the same family of viruses that causes measles, mumps, and bronchiolitis in humans). The disease is highly contagious via inhalation. Morbidity and mortality may vary greatly among animal species, with up to 100% mortality in unvaccinated populations of ferrets. In domestic dogs, while the acute generalized form of distemper has a high mortality rate, disease duration and severity depend mainly on the animal's age, immune status, and the virulence of the infecting strain of the virus. Despite extensive vaccination in many regions, it remains a major disease in dogs and was the leading cause of infectious disease death in dogs prior to a vaccine becoming available.

The origin of the word distemper is from Middle English distemperen, 'to upset the balance of the humors,' which is from Old French destemprer, 'to disturb,' which is from Vulgar Latin distemperare, 'to not mix properly.'

In Europe, the first report of CDV occurred in Spain in 1761. Edward Jenner described the disease in 1809, and French veterinarian Henri Carré determined that the disease was caused by a virus in 1905. Carré's findings were disputed by researchers in England until 1926, when Patrick Laidlaw and G.W. Dunkin confirmed that the disease was, in fact, caused by a virus.

The first vaccine against canine distemper was developed by the Italian Vittorio Puntoni. In 1923 and 1924, Puntoni published two articles in which he added formalin to brain tissue from infected dogs to create a vaccine that successfully prevented the disease in healthy dogs. A commercial vaccine was developed in 1950, yet owing to its limited use, the virus remains prevalent in many populations.

The domestic dog has largely been responsible for introducing canine distemper to previously unexposed wildlife and now causes a serious conservation threat to many species of carnivores and some species of marsupials. The virus contributed to the near-extinction of the black-footed ferret. It also may have played a considerable role in the extinction of the thylacine (Tasmanian tiger) and recurrently causes mortality among African wild dogs. In 1993–1994, the lion population in the Serengeti, Tanzania, experienced a 20% decline as a result of the disease. The disease has also mutated into the phocine distemper virus, which affects seals.

In dogs, signs of CDV vary widely, from no signs to mild respiratory signs indistinguishable from kennel cough to severe pneumonia with vomiting, bloody diarrhea, and death.