A breed standard is a written and published document intended to describe the characteristics and traits of an animal breed that make it uniquely distinguishable from other breeds or from mongrels.

Although the idea may have originated in the desire simply to describe the nature of particular canine varieties, in the hands of The (English) Kennel Club and its various imitators in other countries, it came to be regarded both as a "blueprint" to guide breeders and as a "standard of perfection" to facilitate the evaluation of dogs at dog shows. In this way, what began as a secondary and merely descriptive item, purely a matter of information, became a rigid rule-book that encouraged inbreeding, extremes of artificial selection, elitism, and the continual exaggeration of points of superficial, visible breed type as developed in the concept of "conformation" judging at dog shows.