As reproductive performance is an important criterion in animal production, there is considerable interest in prolific breeds. Certain prolific breeds of sheep produce an average of more than two lambs per pregnancy. With the "discovery" of the Finnsheep and Romanov breeds, followed in the 1980s by the discovery of the Booroola gene in Australia, research into prolificacy has escalated. Also, artificial insemination and embryo transfer techniques now make it easier to move prolific breeds across continents and incorporate prolificacy into local populations. There have also been a number of recent studies on the physiology, nutrition and management of prolific sheep. Previously there has been no single book reviewing and collating this current knowledge. This book fills the gap and covers all aspects of the subject, including descriptions of the various breeds. Written by authors from every region of the world, the book is a comprehensive work on this subject.