Fructo-oligosaccharides or inulin-type fructans are mixtures of oligomers that are composed primarily of β-D-fructose monomers linked by β2-1 osidic bonds. They are natural constituents of many edible plants. They resist digestion and are not absorbed in the upper part of the gastrointestinal tract, but they are fermented in the colon. That fermentation produces short-chain fatty acids, which acidify the colonic content; increase bacterial biomass and, consequently, fecal mass; and modify the composition of the microflora, especially by stimulating the growth of bifidobacteria. Fructo-oligosaccharides are thus prebiotics and a method of the Association of Official Analytical Chemists exists to measure them in food products. Because of this behavior in the gastrointestinal tract, inulin-type fructans have a low caloric value compared with carbohydrate absorbed in the small intestine, they improve Ca absorption and Ca balance, and, at least in experimental models, they inhibit the development of chemically induced aberrant crypt foci. Moreover, at a systemic level, they may contribute to modulating lipogenesis and reducing triglyceridemia. The data reviewed in this article support the classification of inulin-type fructans as functional food ingredients for which claims will or should become authorized when data for humans become available.