Treg cells are critical for the maintenance of immune homeostasis and suppression of naturally occurring self‐reactive T cells; however, in order to induce suppression Treg cells must first be activated via their T‐cell receptor by recognition of specific antigen–MHC complexes. In this issue of the European Journal of Immunology, Föhse et al. [Eur. J. Immunol. 2011. 41: 3101–3113.] shed light on the important question of the role of TCR diversity on Treg‐cell function by demonstrating that high TCR diversity is crucial for optimal Treg‐cell expansion, peripheral reshaping of the Treg‐cell TCR repertoire and in vivo suppressive capacity. In this Commentary, we discuss these findings and also propose a simple mathematical model to aid in the understanding of the relationship between Treg‐cell TCR diversity and the level of suppression delivered by Treg cells in vivo.