Understanding the biological role of the diverse oligosaccharides of glycoproteins and glycolipids has been a major challenge in cell biology. Glycosylation is an essential step during molecular recognition and is involved in protein folding, sorting, targeting and intracellular translocation. Further, glycoproteins of the cell membrane play a major role in cell adhesion, hormone function, antibody action and signal mediation. Current knowledge of the molecular and cellular mechanisms involved in these processes is presented.