The involvement of CD4+CD25+ regulatory T cells (Treg) in general immune homeostasis and protection from autoimmune syndromes is now well established. Similarly, there has been increasing evidence for Treg involvement in allograft rejection and current immunotherapies. However, despite significant advances in understanding the development, function, and therapeutic efficacy of Treg in certain well-defined rodent models, the relevance of Treg to clinical transplantation remains unclear. In this review, we summarize our current understanding of the role of Treg in immunity and organ transplantation in experimental and clinical settings. In addition, we review advances in using Treg as a form of immune therapy. The goal is to highlight the complexities and opportunities in the field and to provide evidence to support the use of antigen-specific Tregs in the context of transplantation to facilitate a robust and selective state of immune tolerance.