Interferons are cytokines that are very important in regulating both innate and adaptive immune response. Of the two different types of interferons, Type I interferons are potent mediators of the innate immune response against viruses and cancer. Type II interferons, mainly IFN-y enhances T cell polarisation in the lymph nodes that result in their expansion. This book discusses the characterisation, mechanisms of action and clinical applications of interferons. Topics include interferon-gamma, oligodendrocyte injury and inflammatory demyelination; the role of IFN-y in oesophageal squamous cell carcinoma; interferons in multiple sclerosis; the effect of interferons on NK cell activity in HIV infection and tumour cell development; and understanding the mechanisms of interaction between serine proteases, serine protease receptors and interferons.