Mifepristone (RU486), the first clinically available antiprogestin, has generated great interest since its discovery in the early 1980s. Today, it is recognized that mifepristone, along with other antiprogestins, has a potentially significant therapeutic role in human health and disease, with likely applicability to a variety of pregnancy-related conditions (e.g., management of labor) and to contraception, endometriosis, and cancer, among others. But because mifepristone has been studied and used most widely as a means of nonsurgical abortion, political issues have thus far limited research on the drug and prevented its introduction into the U.S. market. This book provides an unbiased evaluation of current knowledge about both the fundamental nature of antiprogestins as well as their possible use in treating numerous diseases and conditions, and it contains recommendations for future research.