Compared to total allergenic extracts, recombinant allergens available for specific IgE measurement represent an important advance in the diagnosis and treatment of IgE-mediated allergies. Recombinant allergens lead to define the sensitization profile of allergic patients, to identify markers of sensitization and to understand better polysensitivities related to cross-reactions and markers of severity of allergic reactions. They also contribute to the decision to establish tolerance induction (allergen specific immunotherapy) and the optimal selection of the allergenic composition of the vaccine.