The American Cocker Spaniel is a breed of sporting dog. It is a spaniel type dog that is closely related to the English Cocker Spaniel; the two breeds diverged during the 20th century due to differing breed standards in the US and the UK. In the United States, the breed is usually called a Cocker Spaniel, while elsewhere in the world, it is called an American Cocker Spaniel to distinguish it from its older English cousin. The word cocker is commonly held to stem from their use to hunt woodcock in England, while spaniel is thought to be derived from the breed's origins in Spain.

A spaniel is a type of gun dog. Spaniels were especially bred to flush game out of denser brush. By the late 17th century, spaniels had been specialized into water and land breeds. The extinct English Water Spaniel was used to retrieve water fowl shot down with arrows. Land spaniels were setting spaniels—those that crept forward and pointed their game, allowing hunters to ensnare them with nets, and springing spaniels—those that sprang pheasants and partridges for hunting with falcons, rabbits and smaller mammals such as rats and mice for hunting with greyhounds. During the 17th century, the role of the spaniel dramatically changed as Englishmen began hunting with flintlocks for wing shooting. Charles Goodall and Julia Gasow (1984) write that spaniels were "transformed from untrained, wild beaters, to smooth, polished gun dogs."