Over the last several years, immunologists have re-discovered the importance of regulatory lymphocytes, formerly termed ‘suppressor cells’. Many recent reports have documented their existence, effector functions and potential therapeutic benefits in autoimmunity and transplantation. However, even though modern techniques have allowed us to get a much more detailed picture of these cells, they are still highly controversial. Several unresolved issues responsible for this dilemma are discussed in this book: it is difficult to grow and clone such cells, their phenotypes and effector functions are diverse and can sometimes easily be lost, and it is not well understood how they interact with antigen-presenting cells.This book contains contributions from leading investigators from around the world, including lively discussion of the current state of the art in studies of regulatory lymphocytes. The topics featured are the physiological control of autoimmunity, the role of antigen-specific cells in various diseases and disease models and effector mechanisms. Therapeutic applications are considered, particularly for type 1 diabetes, tissue transplantation and the control of viral infection. This important and groundbreaking book should be of interest to all immunologists.