Kennel clubs are national organisations for recognised breeds of dogs. Kennel Clubs of different countries recognise different breeds and have different breed groups. A recognised breed of dog according to a Kennel Club is a purebreed dog.
The role of a National Kennel Club is to maintain the breed standards so that dogs bred conform to the specifics of there particular breed. Kennel Clubs also act as registries of adult purebred dogs and puppies born to those dogs as well as recording the pedigrees of dogs.
Kennel Clubs also set the rules for the main Dog Shows and Trials.
The Fédération Cynologique Internationale is the International Kennel Club and has members from 80 countries.
The biggest and most well known of the English speaking National Kennel Clubs:
American Kennel Club
Australian National Kennel Council
Canadian Kennel Club
The Kennel Club (United Kingdom)
On this web site I primarily use the Kennel Club groupings, because thats's where I'm from. :)