Regulatory T (Treg) cells are emerging as key players in the regulation of different immune responses, thereby representing potential candidates for therapeutic interventions in a broad variety of immunological disorders. While the reduction or loss in function would be of benefit during the treatment of cancer, induction and/or expansion of Treg cell function might be helpful to interfere with unwanted immune responses in transplantation medicine, during autoimmunity, allergy and inflammation. However, a better understanding of Treg cell biology is a prerequisite to specifically modulate its function during immune responses in vivo. In the present review we will discuss current concepts on different cell types, components and some novel surface receptors expressed by Treg cells, namely Neuropilin-1, CD83 and G protein-coupled receptor 83 which might represent promising targets for the modulation of Treg cell function in human disease.