Regulatory T cells (sometimes known as suppresser T cells) are a specialised sub-population of T cells that act to suppress activation of the immune system and thereby maintain immune system homeostasis and tolerance to self-antigens. This book presents topical research in the study of regulatory T cells, including the role of regulatory T cells in the treatment of multiple sclerosis and hepatocellular carcinoma; genetic engineering of antigen-specific regulatory T cells; regulatory T cells in arthritis, allergic disorders and immunomodulation; and the roles of immunoregulatory cells and the mechanisms of immune response.