Clonal animals, that is those that are genetically identical, are of great importance in biology. The supposed evolutionary advantages of sexual versus asexual reproduction are one of the central paradoxes of current evolutionary theory. The evolved strategy of asexual reproduction includes a large number of diverse species in many different groups, for example aphids, guppies, planktonic rotifers and others. This book draws together many aspects of the functional biology of clonal animals, from their taxonomy and feeding ecology to their life-histories and evolutionary biology. The mechanism of somatic division and parthenogenesis and the benefits of cloning to a variety of Metazoa are examined. Together with a consideration of obligate cloning and modular organisms, this book should be a valuable reference for biologists with an interest in genetics, ecology and evolutionary biology.