Regulatory T cells (T_reg cells) present a unique T-cell lineage that plays a key role for the initiation and maintenance of immunological tolerance. T_reg cells are characterized by the expression of the forkhead box transcription factor Foxp3, which acts as a lineage-specifying factor and determines the unique properties of these immunosuppressive cells. Work over the past few years has shown that well-defined and precisely controlled events on transcriptional and epigenetic level are required to ensure stable expression of Foxp3 in T_reg cells. More recent work suggested that in addition to stable Foxp3 expression, epigenetic modifications of T_reg-cell specific genes contribute to the unique phenotype of T_reg cells by imprinting their transcriptional program and stabilizing the expression of molecules being essential for the suppressive properties of T_reg cells. In this review, we will highlight how Foxp3 expression itself is epigenetically and transcriptionally controlled, how the T_reg-cell specific epigenetic signature is achieved, how Foxp3 as transcription factor influences the gene expression programs in T_reg cells and how unique properties of T_reg-cell subsets are defined by other transcription factors.