IL-17A and IL-17F are important members of the IL-17 family of cytokines that regulate innate and adaptive immunity. IL-17A is associated with chronic inflammatory and autoimmune diseases, and anti-IL-17A antibodies have shown significant clinical efficacy in patients with psoriasis and psoriatic arthritis. IL-17A and IL-17F are homodimeric cytokines that also form IL-17A/F heterodimers, and their precise roles in health and disease remain elusive.