In eukaryotic cells, the interface between the extracellular space and the intracellular matrix is formed of a lipid bilayer in which structural or functional proteins are anchored. Carbohydrates also form components of the cell surface, as glycoconjugates, i.e. glycolipids or glycoproteins. Although the carbohydrate moieties account for a minor part in mass (5–10%), their location at the external face of the membrane confers upon them unique biological functions as ‘recognition signals’.