This volume focuses on various aspects of interleukin-27 (IL-27), especially its potential for clinical applications. The authors discuss the downstream signaling from the IL-27 receptor and its molecular targets in immune cells including Th1, Th2, Th17, Treg, Tr1, Tfh, B cells, DCs and macrophages. The inhibition of Th17 cells by IL-27 is vital for the maintenance of the feto-maternal tolerance and the prevention of lupus, multiple sclerosis, autoimmune uveitis, immune thrombocytopenia and atherosclerosis. However, the same inhibitory capabilities compromise the immune response to bacterial pathogens, and IL-27 is a pathogenic factor in sepsis and tuberculosis. Also covered are the conflicting reports on the role of IL-27 in rheumatoid arthritis, the effect of IL-27 on epithelia, which seems to play a role in asthma, psoriasis and inflammatory bowel diseases, and the direct cytotoxic and anti-vascular effects of IL-27, which make it a promising agent for the treatment of cancer. Accordingly, this volume will be of interest to researchers and clinicians alike.