Summary: The interleukin-17 (IL-17) family consists of six cytokines in mammals. Among them, IL-17 and IL-17F are expressed by a novel subset of CD4+ helper T cells and play critical function in inflammation and autoimmunity. IL-17E, also called IL-25, has been associated with allergic responses. Here, I summarize recent work by my laboratory as well as other investigators in understanding the regulation and function of these three cytokines. From these studies, IL-17 family cytokines may serve as novel targets for pharmaceutical intervention of immune and inflammatory diseases.