Expanding from the classic use of immunosuppressants in transplantation and rejection, this current overview highlights their new roles in clinical medicine. Immunosuppressants are at the forefront of new treatment modalities. Individual chapters focus on their use not only in prevention or treatment of transplant rejection, but also on their use in immune-complex and autoimmune diseases, including rheumatoid arthritis; on combination therapies to achieve synergy in immunosuppression; on new drugs, low molecular weight chemicals, the use of antibodies and gene therapy; on immunological tolerance to prevent or inhibit transplant rejection; and how data derived from transplant studies can be applied to other avenues of immunosuppression. Clinicians and researchers will appreciate the scope of the work and the presentation of new approaches in the rapidly developing field of immunosuppression.