Allergic diseases, including asthma, are chronic inflammatory disorders originating from an aberrant immune response to innocuous antigens in our environment (allergens). In susceptible individuals, sensitization to allergen leads to the induction of allergen-specific T-helper type 2 (Th2) responses and immunoglobulin E (IgE) production. Subsequent challenge with allergen results in IgE-mediated mast cell activation and the recruitment and activation of effector cells, leading to clinical symptoms of disease. In this review, we discuss evidence that the anti-inflammatory cytokine interleukin-10 (IL-10) offers therapeutic promise for the control of asthma and allergy. We highlight the potential role of IL-10 secretion by a specialized T-cell subset, T regulatory cells, to prevent allergic inflammation in healthy individuals and to provide long-term relief from disease symptoms in allergic patients.