The progressive understanding of the nature and mechanisms of T regulatory (Treg) cells in the last decade has changed the concept of immune tolerance, that is no longer considered as a mere lack of immune reactivity but as a finely regulated process that requires specific activity of cells, adhesion and secreted molecules. Tregs play a key role in maintenance of self-tolerance and induction of tolerance against ubiquitous innocuous non-self antigens, so preventing the onset of autoimmune diseases and allergies. This review will focus on the Treg response in allergy that is characterized by a down-regulation of allergen specific T cell proliferation and inhibition of both Th1 and Th2 cytokines production. Hence, Treg cells suppress allergen-specific Th1 and Th2 cell responses playing an important role in the physiological immune response to allergens. Further, Treg cells are able to suppress IgE production by B lymphocytes and directly or indirectly inhibit the activity of allergic inflammation effector cells, namely eosinophils, basophils and mastcells. Finally, increasing evidence suggests that Treg cells are also implicated in chronicity development of inflammatory diseases. This appears to happen through a fine interaction they entertain with resident tissue cells and has been particularly highlighted in the study of airways remodeling in asthma. The understanding of the mechanisms underlying allergen tolerance has brought new interest in the development of new allergy treatment, able to target Treg cells, both in allergy prevention and in the therapy of established allergy.