The terrier is a group of dog breeds initially bred for hunting and killing vermin. While usually small, these dogs are brave and tough with a lively, energetic, and almost hyperactive personality. The largest breed in this family is the Airedale Terrier.

Most terrier breeds were developed in the British Isles. They were used to control rats, rabbits, and foxes both over and under the ground. Some larger terriers were also used to hunt badgers. In fact, the word terrier comes from the Middle French terrier, derived from the Latin terra, meaning earth. The Kerry Blue Terrier and Airedale, however, are particularly noted for tackling river rats and otters in deep water.

Scent hounds are hounds that primarily hunt by scent rather than sight. They are generally regarded as having some of the most sensitive noses among canines.

These dogs 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, the better to process scent. 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 through woodland.

A toy dog is a very small dog kept as a pet, as compared to a very small working dog, although both pet and working dogs can be very small. When an all-breed association or kennel club divides dog breeds into groups for purposes of competition, the Toy Group contains most of the smallest dog breeds in the club's registry.

The use of the word "toy" to describe small dogs that belong to a toy breed is redundant and also incorrect, suggesting that the breed comes in different sizes—there is no such thing, for example, as a "toy Chihuahua"; all Chihuahuas are toy dogs. (However, some breeds do come in different sizes, such as Poodles, which come in standard, miniature, and toy varieties).

A herding dog or pastoral breed is a dog that either has been trained in herding or that is a member of a breed developed for herding. Some herding breeds work well with any kinds of animals; others have been bred for generations to work with specific kinds of animals and have developed physical characteristics or styles of working that enhance their ability to handle these animals. Commonly herded animals include cattle, sheep, and reindeer, although it is not unusual for poultry to be handled by dogs.

The term "herding dog" is sometimes erroneously used to describe livestock guardian dogs, whose primary function is to guard flocks from predation and theft. Herding dogs do not guard flocks but move them. 

A working dog refers to a canine working animal, i.e. a dog that is not merely a pet but learns and performs tasks to assist and/or entertain its human companions, or a breed of such origin.

The domestic dog's health is possibly one of the best-studied areas in veterinary medicine, since the dog has had such a long and close relationship with humans. Infectious diseases are prevalent in dogs and are important not just from a veterinary standpoint but also because of the risk to public health. The most wellknown example of this is rabies. Genetic diseases are common in dogs due to the selective breeding necessary to produce individual dog breeds. Due to the popularity of both commercial and homemade dog foods, nutrition is also a heavily studied subject.

Dog food is plant or animal material intended for consumption by dogs or other canines. Special dog foods given as a reward, and not as a staple, are known as dog treats.

Some people make their own dog food or feed their dogs meals made from ingredients purchased in grocery or health-food stores; many others rely on commercially manufactured dog food.

There are many different recommendations on what diet is best for dogs. Some people argue that dogs have thrived off of leftovers and scraps from their human owners for thousands of years and that commercial dog foods (which have only been available for the past century) contain poor-quality meats, additives, and other ingredients dogs should not ingest, or that commercial dog food is not nutritionally sufficient for their dogs.

Dog training: the process of teaching a dog (Canis lupus familiaris) to perform certain behaviors under various circumstances and in certain roles on command. It is a general term not describing by itself either what or how the dog is taught.

There are as many areas in which to train as there are methods. Most often certain methods, or combinations of methods are applied to any area of training. Obedience, herding, agility, tracking, retrieving, hunting, guard, and schutzhund are common areas of dog training.

• Teaching a dog basic obedience commands (part of obedience training)
• Teaching a dog to perform tricks casually or for circus acts
• Teaching a guide dog to lead the blind
• Teaching a rescue dog to find victims of a disaster
• Teaching a hunting dog to perform its instinctive behaviors at appropriate times

As pack animals, wild dogs have natural instincts that favor cooperation with their fellow dogs. These instincts have been refined and exaggerated through years of selective breeding by humans, and are manifested in the domestic dog’s adeptness at correctly interpreting and responding to signals given by a human handler. The handler is simply whoever is working with a dog at the time.

Dog owners agree that grooming is an important part of dog care, and proper grooming is essential for dogs that are used in competition. Most recommend grooming a dog frequently, although this is not always possible. However, regular grooming helps to ensure the dog is healthy and comfortable.

The main reasons for frequent grooming include:

• improved health of the skin and coat
• decreases the chance of various health problems such as thrush, scratches, and other skin problems
• cleans the dog
• gives the groomer a chance to check the dog's health