The Bernese Mountain Dog  is a large-sized breed of dog, one of the four breeds of Sennenhund-type dogs from the Swiss Alps. The name Sennenhund is derived from the German Senne  and Hund , as they accompanied the alpine herders and dairymen called Senn. Berner  refers to the area of the breed’s origin, in the canton of Bern. This mountain dog was originally kept as a general farm dog. Large Sennenhunde in the past were also used as draft animals, pulling carts. The breed was officially established in 1907. In 1937, the American Kennel Club recognized it; today, the club classifies it as a member of the Working Group.

The four breeds of Sennenhund, with the original breed name, followed by the most popular English version of the breed name:

Like the other Sennenhunde, the Bernese mountain dog is a large, heavy dog with a distinctive tri-colored coat, black with white chest and rust colored markings above eyes, sides of mouth, front of legs, and a small amount around the white chest. An ideal of a perfectly marked individual gives the impression of a white horseshoe shape around the nose and a white “Swiss cross” on the chest, when viewed from the front. A “Swiss kiss” is a white mark located typically behind the neck, but may be a part of the neck. A full ring would not meet type standard. The AKC breed standard lists, as disqualifications, blue eye color, and any ground color other than black.

Height at the withers is 24–28 in (61–71 cm) for males, while it is 22–26 in (56–66 cm) for females. Weight is 80–120 lb (35–55 kg) for males, while it is 70–110 lb (30–50 kg) for females.

The Bernese mountain dog is slightly longer than it is tall, and it is highly muscular.

The head of the Bernese mountain dog is flat on the top with a moderate stop, and the ears are medium-sized, triangular, set high, and rounded at the top. The teeth have a scissors bite. The legs of the Bernese are straight and strong, with round, arched toes. The dewclaws of the Bernese are often removed. Its bushy tail is carried low.

The breed standard for the Bernese mountain dog states that dogs should not be "aggressive, anxious or distinctly shy", but rather should be "good-natured", "self-assured", "placid towards strangers", and "docile". The temperament of individual dogs may vary, and not all examples of the breed have been bred carefully to follow the standard. All large breed dogs should be well socialized when they are puppies, and given regular training and activities throughout their lives.

Bernese are outdoor dogs at heart, though well-behaved in the house; they need activity and exercise, but do not have a great deal of endurance. They can move with amazing bursts of speed for their size when motivated. If they are sound , they enjoy hiking and generally stick close to their people.Not being given the adequate amount of exercise may lead to barking and harassing in the Bernese.

Bernese mountain dogs are a breed that generally does well with children, as they are very affectionate. They are patient dogs that take well to children climbing over them. Though they have great energy, a Bernese will also be happy with a calm evening.

Bernese work well with other pets and around strangers.They are excellent guardians. They tend to bond with one owner, and are somewhat aloof and 'standoffish.'

Cancer is the leading cause of death for dogs in general, but Bernese Mountain Dogs have a much higher rate of fatal cancer than other breeds; in both U.S./Canada and UK surveys, nearly half of Bernese Mountain Dogs die of cancer, compared to about 27% of all dogs. Bernese Mountain Dogs are killed by many types of cancer, including malignant histiocytosis, mast cell tumor, lymphosarcoma, fibrosarcoma, and osteosarcoma. Inherited medical problems that a Bernese Mountain Dog may face include malignant histiocytosis, hypomyelinogenesis, progressive retinal atrophy, and possibly cataracts and hypoadrenocorticism. The breed is also prone to histiocytic sarcoma, a cancer of the muscle tissue that is very aggressive, and hereditary eye diseases that are common among larger dogs. A four-year-old Bernese with lymphoma named Dylan was one of the first dogs to receive chemotherapy at the Virginia-Maryland Regional College of Veterinary Medicine, and it was successful.

Bernese Mountain Dogs have an unusually high mortality due to musculoskeletal causes. Arthritis, hip dysplasia, and cruciate ligament rupture were reported as the cause of death in 6% of Bernese Mountain Dogs in the UK study; for comparison, mortality due to musculoskeletal ailments was reported to be less than 2% for pure-bred dogs in general. Owners of Bernese Mountain Dogs are nearly three times as likely as owners of other breeds to report musculoskeletal problems in their dogs; the most commonly reported being cruciate ligament rupture, arthritis , hip dysplasia, and osteochondritis. The age at onset for musculoskeletal problems is also unusually low. In the U.S./Canada study, 11% of living dogs had arthritis at an average age of 4.3 years. Most other common, non-musculoskeletal morbidity issues strike Berners at rates similar to other breeds. Prospective Bernese Mountain Dog owners should be prepared to cope with a large dog that may have mobility problems at a young age. Options to help mobility-impaired dogs may include ramps for car or house access, lifting harnesses and slings, and dog wheelchairs . Comfortable bedding may help alleviate joint pain.

The Bernese is one of the short-lived dog breeds, compared both to other breeds of a similar size and to purebred dogs in general. The average life expectancy of a Bernese Mountain Dog is approximately 7 to 8 years. Most other breeds of a similar size have median longevities of 10–11 years. In a 2004 UK survey, the longest-lived of 394 deceased Bernese Mountain Dogs died at the age of 15.2 years.

The Bernese's calm temperament makes them a natural for pulling small carts or wagons, a task they originally performed in Switzerland. With proper training they enjoy giving children rides in a cart or participating in a parade, such as the Conway, New Hampshire holiday parade.Regional Bernese clubs often offer carting workshops.Carting competitions are held for the breed.

On July 1, 2010, the Bernese Mountain Dog became eligible to compete in AKC Herding Events. Herding instincts and trainability can be measured at noncompetitive herding tests. Berners exhibiting basic herding instincts can be trained to compete in herding trials.

Bernese Mountain Dogs shed year-round, and the heaviest shedding is during seasonal changes.[30] Usually the Bernese will only require a brushing once a week, with more in spring and fall, to keep its coat neat and reduce the amount of fur on the floor and furniture. The Bernese will only require a bath about once every couple of months or so, depending on how high its activity level is and how often it spends its time in the dirt.