Although originally described as a potent T cell growth factor in vitro, the main non redundant role of interleukin-2 (IL-2) in vivo is now known to be the maintenance of peripheral T cell tolerance. As well as promoting the proliferation and survival of recently activated effector T cells, IL-2 also plays a critical role in regulatory T cell (Treg) homeostasis and has been variously described as promoting the thymic development, peripheral homeostasis and suppressive function of Tregs. These observations, stemming largely from studies on various murine models of IL-2 and IL-2 receptor deficiency, have prompted a greater understanding of the pro-tolerogenic nature of IL-2 dependent signaling. Here we discuss current knowledge concerning the importance of IL-2 mediated signaling in Treg biology as well as its relevance to possible therapeutic applications.