Endometriosis provides a unique clinical and scientific challenge. It is being diagnosed with increasing frequency and yet we are unsure of the significance of this in many patients. Its appearance varies from a tiny focus of disease to a potently destructive phenomenon. Weare still unsure of the relative value of medical or surgical treatment. The pathogenesis and control of the cellular function of the disease proVide many scientific problems. The presence of a comparative normal epithelium, namely endometrium, provides a unique research opportunity. It is probable that only through basic science research will we be able to solve the clinical dilemmas that endometriosis presents. We felt that it was important to create a book that explored the important scientific and clinical problems. We therefore invited acknowledged experts from both Europe and the United States of America to review their fields. The purpose of these reviews is not only to provide a resource for clinicians and scientists but also to stimulate thought and new ideas for research and treatment. To fulfil that aim we have asked that the authors be more speculative than normal for a volume such as this. We thank them for responding to their task so well and hope that you will feel as stimulated by their efforts as we have been.