IL-23 and Th17 cells are critical in psoriasis development. This study shows that dermal γδ T cells are the main IL-17 producers in skin upon IL-23 stimulation. These cells constitutively express IL-23R, RORγt, and various chemokine receptors. IL-17 production from dermal γδ T cells is independent of αβ T cells. In Tcrd-/- and Il17ra-/- mice, IL-23-induced epidermal hyperplasia and inflammation were significantly reduced, while in Tcrd-/- mice, imiquimod-induced skin pathology was also decreased. IL-23 stimulates dermal γδ T cell expansion. In psoriasis patients, γδ T cells are greatly increased in affected skin and produce large amounts of IL-17. Thus, IL-23-responsive dermal γδ T cells are the major IL-17 producers in the skin and may represent a novel target for psoriasis treatment. Dermal γδ T cells are phenotypically unique, constitutively expressing CCR6 and RORγt, and have a unique TCR Vγ usage. They are also required for IL-23- and IMQ-induced skin inflammation and acanthosis. IL-17R expression is necessary for IL-23-induced epidermal hyperplasia and inflammation. IL-23, but not pathogen products, stimulates in vitro expansion of dermal γδ T cells. Large numbers of IL-17-secreting γδ T cells are present in human psoriatic skin. Dermal γδ T cells are critical IL-17-producing cells in psoriasis. These findings highlight the importance of dermal γδ T cells in psoriasis pathogenesis.IL-23 and Th17 cells are critical in psoriasis development. This study shows that dermal γδ T cells are the main IL-17 producers in skin upon IL-23 stimulation. These cells constitutively express IL-23R, RORγt, and various chemokine receptors. IL-17 production from dermal γδ T cells is independent of αβ T cells. In Tcrd-/- and Il17ra-/- mice, IL-23-induced epidermal hyperplasia and inflammation were significantly reduced, while in Tcrd-/- mice, imiquimod-induced skin pathology was also decreased. IL-23 stimulates dermal γδ T cell expansion. In psoriasis patients, γδ T cells are greatly increased in affected skin and produce large amounts of IL-17. Thus, IL-23-responsive dermal γδ T cells are the major IL-17 producers in the skin and may represent a novel target for psoriasis treatment. Dermal γδ T cells are phenotypically unique, constitutively expressing CCR6 and RORγt, and have a unique TCR Vγ usage. They are also required for IL-23- and IMQ-induced skin inflammation and acanthosis. IL-17R expression is necessary for IL-23-induced epidermal hyperplasia and inflammation. IL-23, but not pathogen products, stimulates in vitro expansion of dermal γδ T cells. Large numbers of IL-17-secreting γδ T cells are present in human psoriatic skin. Dermal γδ T cells are critical IL-17-producing cells in psoriasis. These findings highlight the importance of dermal γδ T cells in psoriasis pathogenesis.