Plant food allergens can be classified into families and superfamilies on the basis of their structural and functional properties. The most widespread groups of plant proteins that contain allergens are the cupin and prolamin superfamilies and the protein families of the plant defense system. The cupin superfamily includes allergenic seed storage proteins of the vicilin and legumin type present in soybeans, peanuts, and tree nuts. The prolamin superfamily includes several important types of allergens of legumes, tree nuts, cereals, fruits, and vegetables, such as the 2S albumin seed storage proteins, the nonspecific lipid transfer proteins, and the cereal -amylase and protease inhibitors. Plant food allergens are also found among the various groups of defense proteins that enable plants to resist biotic and abiotic stress, such as the pathogenesis-related proteins, certain proteases, and protease inhibitors. This review focuses on a classification system of plant food allergens that is emerging from the synopsis of allergology and protein evolution.