The IL-17 family in humans consists of six distinct cytokines (IL-17A-F) that can interact with five IL-17 receptors (IL-17RA-E). The interaction between these cytokines and their receptors are critical in mediating host defenses while also making major contributions to inflammatory and autoimmune responses as demonstrated through both in vitro and in vivo experiments as well as human clinical trials. Inhibition of the IL-17A/IL-17RA interaction by monoclonal antibodies has also displayed remarkable efficacies in clinical trials against psoriasis and other autoimmune diseases. Recently, we and others reported the identification and characterization of both small-molecule and peptide IL-17A antagonists. These non-antibody IL-17A antagonists can effectively and selectively disrupt the IL-17A/IL-17RA complex and may provide alternative modalities to treat IL-17-related autoimmune and inflammatory diseases. This chapter summarizes the reported crystal structures of the IL-17 cytokines, their complexes with IL-17RA, and their complexes with both monoclonal antibodies as well as small-molecule and peptide antagonists.