Scent hounds (or scenthounds) are a type of hound that primarily hunts by scent rather than sight. These breeds are hunting dogs and are generally regarded as having some of the most sensitive noses among canines.
Hounds are hunting dogs that either hunt by following the scent of a game animal (scenthounds) or by following the animal by sight (sighthounds). There are many breeds in the scenthound type, and scenthounds may do other work as well, so exactly which breeds should be called scenthound can be controversial. Kennel clubs assign breeds of dogs to Groups, which are loosely based on breed types. Each kennel club determines which breeds it will place in a given group.
Scent hounds specialize in following a smell or scent. Most of these breeds have long, drooping ears. One theory says that this trait helps to collect scent from the air and keep it near the dog's face and nose. They also have large nasal cavities, which also helps to help them smell better. Their typically loose, moist lips are said to assist in trapping scent particles.
Most of these breeds have deep, booming voices and use them actively when running, and especially when following a scent trail. Although this can be a nuisance in settled areas, it is a valuable trait that allows the dog's handler to follow the dog or pack of dogs during a hunt even when they are out of sight, such as when following a fox or raccoon through woodland.
Scent hounds do not need to be as fast as sight hounds, because they do not need to keep prey in sight, but they need endurance so that they can stick with a scent and follow it for long distances over rough terrain. The best scent hounds can follow a scent trail even across running water and even when it is several days old. Most scent hounds are used for hunting in packs of multiple dogs. Longer-legged hounds run more quickly and usually require that the hunters follow on horseback; shorter-legged hounds allow hunters to follow on foot. Hunting with some breeds, such as German Bracke, American Foxhounds, or coonhounds, involves allowing the pack of dogs to run freely while the hunters wait in a fixed spot until the dogs' baying announces that the game has been "treed". The hunters then go to the spot on foot, following the sound of the dogs' baying.