Since the original introduction by Coca and Coombs in 1923, the concept of atopy has always been linked to the relevance of an inherited predisposition in causing immediate-type hypersensitivity reactions to common allergens. However, the mechanisms underlying this predisposition have long been vague and controversial. Only recently, the better knowledge of the basic pathophysiological abnormalities of atopy as well as the availability of molecular biology techniques for gene mapping, have renewed the interest of several research groups for the genetics of atopy and have produced substantial progress in its understanding.