The cytokine transforming growth factor-β (TGF-β) plays an important role in the maintenance of T cell homeostasis, immune tolerance to self-antigens, and T cell differentiation during immune responses. TGF-β has pleiotropic effects on adaptive immune responses, especially on the differentiation of T helper and T regulatory cell populations, which depends on the T cell differentiation status and the stimulation conditions. This review provides an update about the roles of TGF-β in T cell responses, especially in the regulation of Treg development and biological features under steady state and inflammation. We also discuss the additional roles that TGF-β plays in the development and function of other T helper cells, such as Th1, Th2, Th9, Th17, and Th22 cells during inflammation.