Regulatory T (T(reg)) cells are a unique CD4(+) T cell lineage that plays a crucial role in the maintenance of immunological tolerance. The Forkhead box transcription factor Foxp3 is critically involved in T(reg) cell development and responsible for determining the suppressive function of these cells. The majority of Foxp3(+) T(reg) cells are generated during T cell development within the thymus and show features of a stable T cell lineage. New work indicates that both induction and stabilization of Foxp3 expression are under epigenetic control, which suggests that selective interference with the underlying chromatin remodeling mechanisms might enable the development of future therapeutic strategies targeting T(reg) cells.