The Sussex Spaniel is a breed of dog native to Sussex in southern England. It is a low, compact spaniel and is as old a breed as and similar in appearance to the Clumber Spaniel. They can be slow-paced, but can have a clownish and energetic temperament. They suffer from health conditions common to spaniels and some large dogs, as well as a specific range of heart conditions and spinal disc herniation.

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."