Due to the critical role of forkhead box (Fox)p3⁺ regulatory T cells (Tregs) in the regulation of immunity and the enrichment of Tregs within many human tumors, several emerging therapeutic strategies for cancer involve the depletion or modulation of Tregs, with the aim of eliciting enhanced antitumor immune responses. Here, we review recent advances in understanding of the fundamental biology of Tregs, and discuss the implications of these findings for current models of tumor-associated Treg biology. In particular, we discuss the context-dependent functional diversity of Tregs, the developmental origins of these cells, and the nature of the antigens that they recognize within the tumor environment. In addition, we highlight critical areas of focus for future research.