Increased understanding of the biology of interleukin 17 (IL-17) has revealed that this cytokine is a central player in immunity at the sites most exposed to microorganisms. Although it has been strongly associated with immunopathology, IL-17 also has an important role in host defense. The regulation of IL-17 secretion seems to be shared among various cell types, each of which can concomitantly secrete additional products. IL-17 has only modest activity on its own; its impact in immunity arises from its synergistic action with other factors, its self-sustaining feedback loop and, in some cases, its role as a counterpart of interferon-γ (IFN-γ). Together these attributes provide a robust response against microorganisms, but they can equally contribute to immune pathology. Here we focus on a discussion of the role of IL-17 during infection.