Giant Dog breeds refer to those breeds whose height and weight classified them into largest ends of all dog breeds. Although there are no universal heights or weight breed as giant, some measures will consider them as giants such as weighing from 45 kg to 80 kg when adult and reaching 80 cm at the shoulders. Giant Dogs are popular dogs for their impressive size that arouse admiration aside from being so mellow, gentle and relaxed. Peaceful, affectionate and docile, Giant dogs show absolute devotion to their owners.

They make precious companions for the whole family; they can be good with children. They have remarkable courage; their ruggedness enables them to perform outstanding exploits such as legendary rescues and as excellent helpers for human in many situations.

In August 2004, a Harlequin Great Dane dog named "Gibson" from California was recognized by Guinness Book of Records as the world's tallest dog, measuring 42.2 inches (107 cm) at the withers, he is more than 7 feet tall standing on his hind legs, he's 170 lbs. The 17 common giant dog breeds are divided into 3 main groups:

- Mastiff Type: Bull Mastiff, Tibetan Mastiff, Dogue de Bordeaux, Mastiff, Neopolitan Mastiff, Rottweiler and Great Dane.
- Mountain Dogs: Bernese Mountain Dog, Leonberger, Pyrenean Mountain Dog, Estrela, St. Bernard, Newfoundland.
- Other Types: Anatolian Shepherd Dog, Irish Wolfhound, Komondor, Hungarian Kuvasz, Bloodhound.

The giant dog breeds grow more rapidly comparing to smaller dog breeds; they take longer to mature up to their full adult size, about 18 months to 24 months. Their lifespan is generally shorter than smaller breeds, often living around only 6 years to 10 years of age. Giant expenses more on overall; they eat more and require less exercise than smaller dogs. On health issues, giant dog has common joint problems such as hip dysplasia and arthritis, others where hypothyroidism or low thyroid function and bloat or gastric dilatation. Proper petsafe caring and support can be able to double the life spans of some gentle giant dogs like Great Danes up to 14-18 years. By catering physical and emotional needs of dogs such as like freedom going in and out of the house, just like human, proper feeding, balanced diets, scheduled exercise, caring procedures and out of harm and heat of sun. Enough shelter space is needed for them like giant dog containment fences and large heated dog beds are required to ensure quality rest and comfort.