Oligosaccharides are a complex mixture of approximately 130 compounds present in human milk. It has been shown that human milk oligosaccharides induce an increase in the number of bifidobacteria of colonic flora in breast-fed infants, accompanied with a significant reduction in the number of pathogenic potential bacteria, due to their bifidogenic activity. Complex oligosaccharides have the capacity of inhibiting the binding of pathogens to cell surface because they act as competitive receptors. They are associated with a lower risk of infections and diarrhoea and an improvement of the immune system response. Due to the decrease of the pH intestinal caused by their fermentation, oligosaccharides provoke a reduction of the flora pathogens, an increase of bifidobacteria and an increase of the availability of minerals. In the food industry, simple oligosaccharides such as fructooligosaccharides and galactooligosaccharides are used as bifidogenic oligosaccharides and some infant products contain them in the hope that this might provide some of the benefits attributed to oligosaccharides in human milk. This paper reviews characteristics of oligosaccharides, their beneficial effects and use of oligosaccharides in the food industry. In adults, the benefits of some of the oligosaccharides have been established in several clinical trials, but in infants more fundamental research is needed to establish the metabolic role of these components and the daily intake with bifidogenic activity.