The Southdown is a small, dual purpose British sheep. Today it is raised in many parts of the world. It has evolved into two sub breeds. The Southdown raised by commercial growers today, is somewhat larger than the "traditional" Southdown of years past. The "Baby Doll" Southdowns, on the other hand, have been selected for small size and "cuteness" by a small number of hobby breeders. The Baby Doll breeders claim that their sheep are closer to the old, traditional, British Southdown than are the commercial Southdown sheep being grown today.

The Southdown breed was originally bred by John Ellman of Glynde, near Lewes, East Sussex about 200 years ago. His work was continued by Jonas Webb of Babraham in Cambridgeshire who developed the larger animal that we see today.

It was exported to New Zealand and was used in the breeding of the Canterbury Lamb. The Southdown is recognised by the Rare Breeds society as an "at risk" breed, although today it is popular amongst the smaller scale breeders of sheep. The Southdown Sheep Society promotes this breed.