This review focuses on updated information about alpha-galactosides, their chemical structure, biosynthesis, plant physiological functions, occurrence in foods, positive and negative physiological effects in animals, changes during food processing, and their potential application as prebiotics in the food industry. Although alpha-galactosides are considered as the main flatus-causing factors, they are also involved in several important functions during plant and seed development and beneficially stimulate the growth and activity of living bifidobacteria and lactobacilli in the human colon. We focus here also on legumes as a source of this kind of prebiotics as potential health promoters.