CD4 + CD25 + Foxp3 + T lymphocytes, known as regulatory T cells or T regs , have been proposed to be a lineage of professional immune suppressive cells that exclusively counteract the effects of the immunoprotective "helper" and "cytotoxic" lineages of T lymphocytes. Here we discuss new concepts on the mechanisms and functions of T regs . There are several key points we emphasize: 1. Tregs exert suppressive effects both directly on effector T cells and indirectly through antigen-presenting cells; 2. Regulation can occur through a novel mechanism of cytokine consumption to regulate as opposed to the usual mechanism of cytokine/chemokine production; 3. In cases where CD4 + effectorT cells are directly inhibited by T regs , it is chiefly through a mechanism of lymphokine withdrawal apoptosis leading to polyclonal deletion; and 4. Contrary to the current view, we discuss new evidence that T regs , similar to other T-cells lineages, can promote protective immune responses in certain infectious contexts (Chen et al., 2011;Pandiyan et al., 2011). Although these points are at variance to varying degrees with the standard model of T reg behavior, we will recount developing findings that support these new concepts.