Most jurisdictions that restrict pit bulls, including Ontario, Canada, and Denver, Colorado, use the term "pit bull" to refer to the modern American pit bull terrier, American Staffordshire terrier, and Staffordshire bull terrier. However, a few jurisdictions, such as Singapore and Franklin County, Ohio, also classify the modern American Bulldog as a "pit bull-type dog", while in the United Kingdom the term applies only to the American pit bull terrier. All three breeds share a similar history, with origins rooted from the bulldog and a variety of terriers. The term can also refer to dogs that were known as "bull terriers" prior to the development of the modern Bull terrier in the early 20th century.

Research has been conducted into human fatalities related to pit bull type dogs, due to a number of well-publicized incidents. These incidents resulted in breed-specific legislation being enacted in several jurisdictions. This, in turn, has led to an increase in rates of liability insurance, and in some instances has led to airlines placing restrictions on air travel for pit bulls, though in some instances restrictions are in place for the dogs' own well-being.

Though the pit bull type dogs were all created with similar crossbreeding between bulldogs and terriers, each individual breed within the type has a somewhat different history. There are an estimated 77.5 million owned dogs in the United States; however, the number of pit bull-type dogs has not been reliably determined. Animal shelters in the United States euthanized approximately 1.7 million dogs in 2008; approximately 980,000, or 58 percent of these were assessed to have been pit bull-type dogs.

The American pit bull terrier is the product of interbreeding between terriers and a breed of bulldogs to produce a dog that combined the gameness of the terrier with the strength and athleticism of the bulldog. These dogs were initially bred in England, Ireland, and Scotland, and arrived in the United States with immigrants from these countries. In the United States, these dogs were used as catch dogs for semi-wild cattle and hogs, to hunt, to drive livestock, and as family companions; however, some were selectively bred for their fighting prowess, and starting in the early 20th century, they began to replace the bull terrier as the "dog of choice" for dog fighting in the United States.

The United Kennel Club (UKC) was the first registry to recognize the American pit bull terrier. UKC founder C. Z. Bennett assigned UKC registration number 1 to his own dog, "Bennett's Ring", as an American pit bull terrier in 1898.

American pit bull terriers today successfully fill the role of companion dog, police dog, and therapy dog; however, terriers in general have a higher tendency towards dog aggression and American pit bull terriers constitute the majority of dogs used for illegal dog fighting in the United States. In addition, law enforcement organizations report these dogs are used for other nefarious purposes, such as guarding illegal narcotics operations, use against the police, and as weapons.

The fighting reputation of pit bull-type dogs led the San Francisco Society for the Prevention of Cruelty to Animals in 1996 to relabel pit bull terriers as "St. Francis terriers" (not associated with the "terrier" mascot of St. Francis College in New York) so that they might be more readily adopted; 60 temperament-screened dogs were adopted until the program was halted after several of the newly adopted dogs killed cats. The New York City Center for Animal Care and Control tried a similar approach in 2004 by relabeling their pit bull terriers as "New Yorkies", but dropped the idea in the face of overwhelming public opposition.

The American Staffordshire terrier was the product of 19th century interbreeding between bulldogs and terriers that produced the "bull-and-terrier dog", "Half and Half", and at times "pit dog" or "pit bullterrier" that later assumed the name in England of the Staffordshire bull terrier. The bulldog of that time was different to the modern Bulldog, having a full muzzle and a long, tapering tail; there is some debate as to whether the White English terrier, the Black and Tan terrier, the Fox terrier or some combination thereof were used. These dogs began to find their way into America as early as 1870 where they became known as pit dog, pit bull terrier, later American bull terrier, and still later as Yankee terrier. They were imported primarily, but not exclusively, for pit fighting.

In 1936, they were accepted by the American Kennel Club (AKC) as "Staffordshire terriers". The name of the breed was revised effective January 1, 1972 to "American Staffordshire terrier" since breeders in the United States had developed a type which is heavier in weight than the Staffordshire bull terrier of England and the name was changed to distinguish them as separate breeds.

The Staffordshire bull terrier had its beginnings in England many centuries ago when the bulldog and Mastiff were used for the sports of bull-baiting and bear-baiting; in the Elizabethan era, breeders produced large dogs for these sports but later on the 100–120 pound animal gave way to a small, more agile breed of up to 90 pounds.