The prebiotic fibers, inulin and oligofructose, are becoming increasingly popular in healthy food formulations in the U.S. marketplace. These unique natural dietary fiber products appear on the ingredient legends of more than 400 European food products and more than 1,750 consumer products worldwide. Their success lies in their wide range of health-promoting benefits, from the promotion of calcium and magnesium absorption to improved digestive health. Extensive research has shown that ingestion of moderate amounts of inulin and oligofructose selectively stimulate the beneficial bifidobacteria in the large intestine, while suppressing the growth and presence of less desirable bacteria such as clostridia and salmonella. In animal studies, the stimulation of bifidobacteria growth has been shown to inhibit carcinogens, decrease intestinal pH, reduce harmful bacteria, and boost immunity. Recent studies have shown the positive effects of oligofructose on increasing satiety. This article focuses on the prebiotic properties of inulin and oligofructose as borne out in human studies.