T helper (Th) 17 cells are a recently identified subset of T cells that regulate tissue inflammation, and RORγt and RORα have been shown to be Th17-specific transcription factors that mediate Th17 cell generation. A new study of Batf-deficient mice shows that this AP-1 family transcription factor also regulates Th17 cell differentiation by binding to Th17-associated gene promoters and by maintaining RORα and RORγt expression, shedding new lights on current clinical modulation of Th17 cell function in inflammatory diseases.