T cell homeostasis is required for normal immune responses and prevention of pathological responses. Transforming growth factor beta (TGFbeta) plays an essential role in that regulation. Owing to its broad expression and inhibitory effects on multiple immune cell types, TGFbeta regulation is complex. Through recent advances in cell-specific targeting of TGFbeta signaling in vivo, the role of TGFbeta in T cell regulation is emerging. We demonstrated here a critical role for TGFbeta in regulating effector vs regulatory T cell homeostasis.