Regulatory T cells (TREG) are a subset of CD4+ T cells with a critical role in the prevention of autoimmunity. Whether defects in TREG contribute to the pathogenesis of rheumatoid arthritis (RA) is unclear. However, a variety of approved and experimental drugs for RA may work, in part, by promoting the function or increasing numbers of TREG. Furthermore, animal studies demonstrate that direct injection of TREG ameliorates a wide range of experimental models of inflammatory and autoimmune diseases. Thus, cell-based therapy with TREG has the potential to produce durable disease remission in patients with RA.