Fancy mice are mice that have been selectively bred as pets or for show. They can vary greatly in size, from small pet mice that are approximately 16–18 cm (6–7 in) long from nose to the tip of the tail, to show mice that measure 30 cm (12 in) nose to tail. Pet mice weigh about 25–40 g (0.9–1.4 oz) but large show mice can weigh up to 100 g (3.5 oz).
Human-directed artificial selection in fancy mice has created a wide variety of colors and patterns. These include black, chocolate, blue, white, cream, lilac, red, fawn, champagne, cinnamon, golden agouti, silver agouti, silver and dove. All mouse standards fall into one of five categories: Selfs (one solid color all over), Tans (mice of one solid color on the top with a tan belly), Marked either in Even or Broken patterns (spotting of a standard color on a base of white) and a miscellaneous category.