Quoted from AKC official website
Authorities acknowledge that throughout the world there are several hundred distinct breeds of purebred dogs, not all of which are AKC recognized breeds. Those officially recognized for AKC registration appear in the Stud Book of the American Kennel Club. The AKC provides for a regular path of development for a new breed, which may result in that breed's full recognition and appearance in the official Stud Book as an AKC recognized breed.
Briefly stated, the requirement for admission to the Stud Book is clear and categorical proof that a substantial, sustained nationwide interest and activity in the breed exists. This includes an active parent club, with serious and expanding breeding activity over a wide geographic area.
When in the judgment of the Board of Directors such interest and activity exists, a breed is admitted to the Miscellaneous Class. Breeds in the Miscellaneous Class may compete and earn titles in AKC Obedience, Tracking and Agility events. Miscellaneous breeds are also eligible to compete in Junior Showmanship. They may also compete at conformation shows, but here are limited to competition in the Miscellaneous Class and are not eligible for championship points.
When the Board of Directors is satisfied that a breed is continuing a healthy, dynamic growth in the Miscellaneous Class, it may be admitted to registration in the Stud Book and the opportunity to compete in regular classes.