The Cavalier King Charles Spaniel is a small breed of dog of Spaniel type, usually considered one of the toy dog breeds. It is a small spaniel with a substantial silky coat of moderate length, often with a mild wave, and long ears. Four colours (Blenheim, Tricolour, Black and Tan, and Ruby) are recognized. The breed originated in the 20th century but has its roots in the older King Charles Spaniel of the Restoration.

The Cavalier King Charles Spaniel is perhaps the largest toy breed: though historically a lap dog, modern day fully-grown adults tend to fill a lap rather amply. It is nonetheless quite small for a spaniel, with fully-grown Cavaliers roughly comparable in size to adolescents of more conventional spaniel breeds. Breed standards call for a height between 30 and 33 cm (12–13 inches) with a proportionate weight between 6 and 10kg (10 and 18 lb), although even purebreds commonly grow to 35-40 cm tall with a proportionate weight between 20-25 pounds. Unlike most other spaniels, the Cavalier has a full-length tail, well-feathered with long hair, which is usually not docked, which is typically carried aloft when walking. The Cavalier's head is nearly flat between the ears and has a well defined nose, its eyes are large and round and this gives the dog its characteristic endearing look. Its neck is strong and is slightly arched and its ears are long and drooping and have plenty of feathering. The body of the Cavalier is small but well balanced, this dog moves with a somewhat elegant and royal gait.

The breed naturally grows a substantial silky coat of moderate length. Breed standards call for it to be free from curl, with a slight wave permissible. In adulthood, Cavaliers grow lengthy feathering on their ears, chest, legs, feet and tail; breed standards demand this be kept long, with the feathering on the feet cited as a particularly important feature of the breed.