Despite considerable research over the past several decades, there is at present no systemic method of male contraception that is safe, highly effective and reversible. Numerous classes of compounds have been examined, but only a very few have reached the stage of clinical testing. While hormonal regulation of male fertility with the use of steroids or LHRH analogues, or both, has achieved some degree of success in limited clinical trials, its widespread applicability still depends upon considerable development. Clearly, a totally novel approach to finding ways to control male fertility is needed. Thus, it was considered important to bring together experts from various fields to discuss the latest findings in cellular and molecular biology in relation to the regulatory mechanisms of mammalian spermiogenesis. This book records the proceedings of a symposium co-sponsored by the WHO special programme of research, development and research training in human reproduction and family health international held in Oaxtepec, Mexico. This interdisciplinary approach provides new insights and may lay the foundation for the development of a modern male contraceptive for use throughout the world. The book will therefore be of interest to biomedical scientists interested in cell and molecular biology, pharmacology and drug development.