If you can't decide between a shepherd, a setter, or a poodle, get them all — adopt a mutt. The world's most popular breed of dog is no breed at all. Mixed breeds, random breeds, mongrels, mutts or curs — call them what you will, they make up the majority of the worldwide dog population. Rare is the country where dogs of mixed and usually unknown heritage do not outnumber their blue-blood, purebred relations. In true mixed breeds, the dog's ancestry is next to impossible to predict, although many people can't help but try to guess. That's part of the fun.

Because they're all related, all of the 400 or so breeds are capable of interbreeding. The millions of mixed-breed dogs around the world are a testament to that. Unfortunately, these are the dogs you're likely to find at the local shelter or dog pound, often the result of accidental breeding between two unsterilized dogs.

Often used interchangeably, the terms "mixed breed" and "crossbreed" have slightly different meanings. Unlike mixes, crossbreeds have clear roots — often evident by looking back just one generation. Sometimes produced randomly, but most often planned by breeders, crossbreeds result from the mating or crossing of two dogs with a different but identifiable lineage. Two purebred dogs are sometimes deliberately crossed in hopes of creating a new breed such as the cockapoo, which is one part cocker spaniel, one part poodle. But despite what those who breed and sell crossbreeds might try to tell you, these are not, nor will they likely ever be, recognized as purebred dogs.