Interleukin (IL)-17, the signature cytokine secreted by T helper (Th) 17 cells, plays important roles in host defense against extracellular bacterial infection and fungal infection and contributes to the pathogenesis of various autoimmune inflammatory diseases. Here we review the recent advances in IL-17-mediated functions with emphasis on the studies of IL-17-mediated signal transduction, providing perspective on potential drug targets for the treatment of autoimmune inflammatory diseases.