Mobile genetic elements are present in all organisms. They are a major cause of spontaneous genetic change and are now exploited as important tools for obtaining mutants, isolating genes, and for studying gene expression. A key role of mobile genetic elements is their self-proliferation; they are "selfish-DNA". Nevertheless, they often show a sophisticated symbiosis with the cells they inhabit, with their activities controlled and used to mediate specific biological processes. In this important study of this topic, two chapters address the mechanistic properties of these elements. An important conclusion is that transposable elements, one major class of mobile genetic elements, appear to use the same overall mechanism for their mobility, one identical to that used by retroviruses like HIV. Two chapters deal with the biological population and evolutionary consequences of mobile elements, while another deals with a novel class of bacterial element, the retron. Finally, two chapters provide methodological details on how to use mobile elements as genetic tools. Overall the approach is comparative. The book will appeal to those hoping to use transposable elements as genetic tools, to those interested in the mechanisms leading to genetic change, and to those looking at how these novel elements contribute to the biology and evolution of organisms. It will prove essential reading for postgraduates and researchers in genetics, molecular biology, biochemistry, and cell biology, and can be used as a vital supplementary reading source for undergraduates in these fields.Sherratt, David is the author of 'Mobile Genetic Elements' with ISBN 9780199634040 and ISBN 0199634041.