Several unique waves of ?? T cells are generated solely in the fetal/neonatal thymus, whereas additional ?? T cell subsets are generated in adults. One intriguing feature of ?? T cell development is the coordination of differentiation and acquisition of effector function within the fetal thymus; however, it is less clear whether this paradigm holds true in adult animals. In this study, we investigated the relationship between maturation and thymic export of adult-derived ?? thymocytes in mice. In the Rag2pGFP model, immature (CD24+) ?? thymocytes expressed high levels of GFP whereas only a minority of mature (CD24-) ?? thymocytes were GFP+ Similarly, most peripheral GFP+ ?? T cells were immature. Analysis of ?? recent thymic emigrants (RTEs) indicated that most ?? T cell RTEs were CD24+ and GFP+, and adoptive transfer experiments demonstrated that immature ?? thymocytes can mature outside the thymus. Mature ?? T cells largely did not recirculate to the thymus from the periphery; rather, a population of mature ?? thymocytes that produced IFN-? or IL-17 remained resident in the thymus for at least 60 d. These data support the existence of two populations of ?? T cell RTEs in adult mice: a majority subset that is immature and matures in the periphery after thymic emigration, and a minority subset that completes maturation within the thymus prior to emigration. Additionally, we identified a heterogeneous population of resident ?? thymocytes of unknown functional importance. Collectively, these data shed light on the generation of the ?? T cell compartment in adult mice.