It has only been a short time since the existence of suppressor cells was demonstrated, yet in this period of time a great deal of information has been compiled concerning their basic science and their functions or disordered functions in human disease. This volume is an tempt to clarify the immune mechanisms through which these cells act, their normal functions, and how their functions are disordered in certain disease states. In this volume some rational approaches are proposed to therapy of diseases perceived at least partially due to disordered immune regulation. Particular focus is on the recently emerging field of soluble suppressor factors as a means of providing adoptive immunotherapy in certain situations. I hope that future work in this field will justify the confidence in this approach.