Allergic rhinitis, a risk factor for bronchial asthma, is a global health problem that impairs patients` physical and social activity and consequently their quality of life. Specific Immunotherapy (SIT) involves the administration, subcutaneously or sublingually, of increasing doses of the causative allergen, in order to induce clinical and immunologic tolerance. SIT has been shown to be effective in those with a poor response to conventional drug therapy. Immunotherapy has been shown to have disease-modifying effects and result in long term remission of allergic symptoms and reduces the risk of progression from rhinitis to asthma, as well as the chances of developing new sensitizations to allergens. Injection immunotherapy is a safe treatment for allergic rhinitis with/without mild controlled asthma, provided that it is performed in the context of a harmonious interaction between trained medical personnel and appropriately selected patients. Immunotherapy suppresses early and late responses to allergen exposure by modifying both T-cell and B-cell responses to inhaled allergens. Immune deviation of allergen-specific T cell responses in favour of Th1 and/or the induction of regulatory T cells is crucial in achieving immune tolerance. Increased understanding of the mechanisms of immunotherapy has identified potential biomarkers of the response to treatment and highlighted new therapeutic pathways with potential for even more effective future standardized vaccines.