A cat breed is a recognizable variety of domestic cat. A cat is considered to be of a certain breed if it is true breeding for the traits that define that breed. Only three percent of owned cats in the United States (estimated at 68 million in 1996  belong to a cat breed, and an even smaller percentage of those are suitable as show cats. As in other domestic animals, purebred animals are registered by organizations that set breed standards. In order to register an individual kitten with a cat fancy association, the kitten usually must have two parents of the same breed - who are both registered with that same organization, and themselves meet the breed standard.
As compared to other domestic companion and farm animals, there are relatively few breeds of cats. There are also a more limited set of characteristics that make one breed of cat distinct from another, as compared to most of the other domestic species. Still, just as the would-be dog owner needs to take "breed" into consideration when choosing a dog, the person who is interested in obtaining a cat is best off knowing something about cat breeds.
In the case of dogs, for example, breeds have been widely recognized for more than a thousand years. The traits specified in dog breeds include body shape, head shape, coat colors, hair textures, and even complex behaviors such as pointing the tail at hunting prey or retrieving. The domestic cat has a much smaller range of variable characteristics between individuals than the domestic dog, and this is also true for the "look" of individual breeds of each kind of animal. So, the difference in average size between the biggest healthy individuals of the largest cat breed (the Maine Coon), and the tiniest healthy individuals of the smallest cat breed (the Korat) is on an order of 3 (in terms of lean weight), where as the same relationship in dogs is something like a 100 fold difference between a small Chiuaua and a large Great Dane.
Some biologists have speculated that cat breeds are really only a matter of different coloring, except for a very few structural features, like the concave face of an extreme Persian. Stephen Budiansky, in expressing this view, has said " genetically, any given cat breed represents nothing more than the fixing of a particular few of the color and coat genes in a breeding line so that they are passed on consistently to the offspring" . At the present time the Cat Genome Project  is attempting to map the genes of the domestic cat. This project is run by the National Cancer Institute in the United States and is aimed mostly towards basic science goals in medicine and biology rather than the specific interests of cat breeders and owners. However, eventually the information gleaned from this project may help pin down just what is different in the gene pool of each type of cat breed.
At present, there are a few things we can say for sure that are true of the breeds of domestic cats.
When populations of cats are isolated by geography or other factors, alleles for unusual traits sometimes concentrate in the group that bestow a recognizable "look" (phenotype). The cats in such a group show special features that breed true among them. These natural breeds of cats include (among others) the Manx, which originated on the Isle of Man, the Turkish Van and the Turkish Angora, the two native breeds of Turkey, and the Maine Coon Cat of the northeastern United States.
Registered purebred breeds
In Europe and North America, the whole concept of cat breeds is a relatively new one. Two hundred years ago there was no such thing as a registered cat breed, however today there are almost a hundred cat breeds. Unlike most kennel clubs, several major cat fancy organizations register cats in breeds that are open to matings between cats in which one parent is of a different breed of cat, or of no designated breed at all (house cat, "alley cat"). This practice probably reflects the fact that many cat breeds are recently developed.
As in other breeds of animal, the look of a top show animal can change over time. For example, in cats, the Persian breed has had marked changes in body type and face shape over the last fifty years.
Over the last XX years, the number of recognized breeds has expanded tremendously.
Currently developing cat breeds
Understanding just how a "new" cat breed comes into being helps illustrate the whole notion of what a breed of cats actually means to a cat fancier.
The munchkin has been called" the feline version of the dachshund". (reference for quote: James R. Richards D.V.M., ASPCA Complete Guide to Cats: Everything You Need to Know About Choosing and Caring for Your Pet. Chronicle Books LLC 1999 ISBN-13 978-0-8118-1929-9) See selective breeding for more in-depth detail on purebred animals.
- (Feline) kings of the castle. By: Cravatta, Matthew. American Demographics, Aug97, Vol. 19 Issue 8, p30, 2p, 1c; (AN 9710132348))
- (reference for quote: The Character of Cats: The Origins, Behavior, and Strategems of Felis silvestris catus Viking, Penguin Group, New York, 2002, ISBN 0-670-03093-7, page 60)