In this review, clinical and epidemiological aspects of milk allergy along with current data on the structure and function of the main cow's milk allergens, are presented. Milk allergy is the most frequent food allergy in childhood. One of the reasons why allergy to cow's milk shows its highest prevalence in children is its early introduction into the diets of infants when breast feeding is not possible. The major allergens are caseins, a-lactalbumin and β-lactoglobulin, but allergies to other minor proteins (immunoglobulins, bovine serum albumin) have also been reported. Milk allergenicity can be reduced by various processing methods (mainly hydrolysis), and processed formulas based on cow's milk can often be safely introduced to children allergic to milk proteins. Cross reactivity has been described between different mammalian milks and between milk and meat or animal dander.