This Review covers the sources and the main effects on human health of well-known micronutrients such as minerals and vitamins and also of microconstituents contained in the Mediterranean diet. Vitamins were first identified because of deficiency diseases still present in certain parts of the world. Hydrosoluble vitamins, among them folic acid and vitamin C, also play a role in chronic degenerative diseases, not only the main cause of mortality in the Western world but also increasingly common in developing countries. Hydrosoluble vitamins are well represented in the Mediterranean diet, more so than vitamin A, a liposoluble vitamin obtained primarily from animal foods. Vitamin E is important for antioxidant and cellular functions. The Mediterranean diet is also rich in provitamins A, such as alpha- and beta-carotene and beta-cryptoxanthine. Microconstituents are non-nutritional compounds known to protect plants and more recently suspected to have a protective effect in humans. They play a role in the antioxidant defense of the organism, but their effect on various enzyme activities appears even more promising and is still under investigation. It is nevertheless difficult to isolate the effect of the numerous biofactors present in the Mediterranean diet from the foods themselves, especially because of the possible synergy between the various biofactors.