The Westminster Kennel Club Dog Show is one of a handful of benched shows in the United States. Dogs are required to be on display in their assigned locations (show benches) during the entire show except when shown in the ring, groomed for showtime, or taken outside for elimination. This type of presentation allows spectators and breeders alike to have an opportunity of seeing all the entered dogs. (In the more common unbenched shows, dogs are required to be present only at assigned ring times.)
The first Westminster show took place on May 8, 1877, making it second only to the Kentucky Derby, in terms of continuously held sporting events in the United States. (Both events were held despite the Great Depression, World War, and pandemic years.) The show originated as a show for gun dogs, primarily Setters and Pointers, initiated by a group of hunters who met regularly at the Westminster Hotel at Irving Place and Sixteenth Street in Manhattan. They decided to create a kennel club called the Westminster Kennel Club specifically to hold a dog show. The prizes for these first shows included such items as pearl-handled pistols, which were of use to the hunters and terriermen who worked these dogs in the field.
Held at Gilmore's Garden (Madison Square Garden) the Westminster show drew over 1,200 dogs. It proved so popular that it took four days instead of the three days originally scheduled. The club donated proceeds from the fourth day to the ASPCA for creation of a home for stray and disabled dogs.
The Westminster Kennel Club predates the formation of the American Kennel Club by seven years and became the first club admitted to the AKC after AKC's founding in 1884. Breed parent clubs (e.g., the Collie Club of America) create the standards for judging their breeds, with the AKC administering the rules about shows and judging.
Dogs are judged by how closely they conform to a written description of the ideal specimen of that breed (the breed standard). While many breeds no longer need to perform their original jobs and are bred mostly for companionship, they are still judged on their innate ability and physical makeup to perform their original jobs. Standards also include items that seem somewhat arbitrary such as color, eye shape, tail carriage, and more.
Today, Westminster takes place over two days and nights in June. During the day, the dogs compete against other dogs of the same breed at Piers 92 and 94. Each Best of Breed winner (BOB) advances to the Group level. There are seven groups: Sporting, Hound, Working, Terrier, Toy, Non-Sporting, and Herding. Group competition occurs during the evenings at Lyndhurst. The seven Group winners advance to Best in Show, the final round of the show. During Best in Show, also held at Madison Square Garden, a judge will select one of judging them as the Best In Show winner. Since 2014, the show allowed mixed-breed dogs to compete in an agility event.
Westminster has held competitions in Junior Showmanship for handlers ages 9-18 since 1934. The eight finalists all receive scholarships for post-secondary schooling. The Club, through the Westminster Kennel Foundation also awards veterinary school scholarships for students from six schools yearly.
The winning dog becomes "America's Dog" for the coming year. The reign begins with a media tour on the day following the show. Following the tour, the winner makes appearances on nearly all television network morning shows and visits the Observation Deck at the Empire State Building. The New York Stock Exchange also invites the winner and related handlers to ring the opening bell.
The event was widely celebrated in New York City every February. The Empire State Building salutes the show by lighting its tower in the Westminster colors of purple and gold for the duration of the show. Saks Fifth Avenue features a street window with a Westminster-themed display. It is unknown if the traditions will continue as the event was moved to Tarrytown in 2021.
During the 2019 broadcast, broadcast rights holder Fox Sports was reprimanded by dog show sponsor Purina when a broadcast voice-over used to introduce a dog group was recorded by NASCAR Cup Series champion Kyle Busch, who is sponsored by a direct competitor, Mars Petcare, as part of an overall sponsorship of Busch through both Mars Inc. candies and pet foods.
From 1984 until 2003, Universal's USA Network broadcast the Westminster Kennel Club Dog Show. Following Universal's acquisition by General Electric in 2003 to form NBC Universal, from 2004 until 2016, the show aired under the NBC Sports label. From 2006 through 2016, the Monday coverage was aired by business news channel CNBC due to conflicts with WWE Raw on the USA Network. On July 28, 2015, Fox Sports announced that it had acquired rights to the event under a 10-year deal beginning in 2017. For the first three years, Fox Sports 1 and Nat Geo Wild provided joint coverage the show.
During NBC's coverage from 1990 to 2016, David Frei co-hosted the event with partners, Al Trautwig (1990-1991, 1993), Bud Collins (1992), Joe Garagiola (1994-2002), Mark McEwen (2003-2004), Lester Holt (2005, 2007-2008), Debbye Turner (2006), Mary Carillo (2009, 2011-2016), and Tamron Hall (2010).
Frei provided the commentary of the 140th event for his final time.
The 141st event in 2017 marked the beginning of the Fox Sports contract. There are two sets of hosting teams. From 2017-19, coverage aired on Fox Sports 1 and National Geographic Wild. For 2017, daytime breed judging was hosted by Justin Kutcher, Paula Nykiel and Jason Hoke and primetime coverage hosted by Chris Myers and Gail Miller Bisher. In 2018, daytime bred judging was hosted by Kutcher, Kimberly Meredith Cavanna and Don Sturz in 2018, while Hoke joined the evening booth of Myers and Bisher. In 2019, the judging experts were swapped, with the day event hosted by Kutcher, Cavanna, and Hoke and evening event by Myers, Bisher, and Sturz. 
Following the acquisition of National Geographic TV Channels and the Fox TV Studios by the Walt Disney Company in 2019, event coverage in 2020 was limited solely to the two Fox Sports channels, Fox Sports 1 for primetime and Fox Sports 2 for daytime judging. John Strong replaced Kutcher as host for daytime breed judging and Fox hosts were Myers, Bisher, and Sturz.
In 2017, Fox Sports 1 aired a one-hour documentary, Crowned: Inside the Westminster Dog Show.
For 2021, the final night judging will be broadcast live on the Fox broadcast network.
In 1884, the AKC began requiring that all dog participants be registered with the AKC and recognized for conformation show competition. In 2016, there are 199 breeds and varieties eligible for Westminster. Because of the show's popularity and prestige, starting in 1992 the AKC limited entries by requiring that dogs must have already earned their breed championship before appearing at Westminster. Later, the Westminster Kennel Club amended that rule - dogs only need one of the two required "major wins" towards their championship titles. However, they don't need to be finished champions to enter.
For the 2020 show the requirement that a dog be a Champion was reinstated by the Westminster Kennel Club and the entry limit decreased to 2500. The conformation show was also spread over 3 days instead of the traditional 2 days, due to the unavailability of one of the usual venues for the event. 
The top five dogs in each breed (based on breed points earned in AKC conformation showing through October 31 of the preceding year), as well as the Best of Breed winner from each breed's national specialty show, receive printed invitations by mail and are eligible for early entry. After that entry deadline passes, other dogs with at least one "major win" may enter, up to a cut-off entry total of 2800 dogs.
There is no prohibition against a winner competing again in future Westminster shows. Seven dogs have won multiple Westminster championships: six dogs in consecutive years (including Warren Remedy, the only three-time champion of the event) and one dog in non-consecutive years. Since 1972, however, there have been no repeat winners. (See List of Best in Show winners of the Westminster Kennel Club Dog Show.)
Dogs of all breeds, including mutts, may participate in the show's agility competition. There is a title for the highest-ranking mutt in the agility round - the "All American Dog."
Through the 134th Westminster Show (February 2010), Best in Show has been won by the Terrier group 45 out of the 103 times that the prize has been awarded since 1907, more than twice as many wins as any other group. The single breed that has won the most is the Wire Fox Terrier, which has won 14 times. Two of the most popular dog breeds in the United States have never won Best in Show - they are the Labrador Retriever and the Golden Retriever.
The oldest dog to win Best in Show was a Sussex Spaniel named Ch. Clussexx Three D Grinchy Glee (a.k.a. Stump), at ten years of age in 2009. The youngest dog to win was a Rough Collie named Laund Loyalty of Bellhaven, at nine months old in 1929. One dog, a Smooth Fox Terrier named Ch. Warren Remedy won Best in Show three times (1907-1909), and six other dogs have won twice. Males have won Best in Show 68 times as opposed to females who have won 35 times.
Following is a list of WKC Best in Show winners since 1990.