This chapter summarizes the biochemical mechanisms for the events occurring in each of the different cellular compartments, namely, the endoplasmic reticulum, Golgi apparatus, condensing vacuoles, and secretory granules. It aims to distinguish three types of glycosylation: the completion of N-glycosidic-linked oligosaccharides, the biosynthesis of oligosaccharides which are attached to the protein by O-glycosidic linkages, and the addition of glycosaminoglycans to proteoglycans. Glycoproteins contain both N- and O-glycosidic linkages between the polypeptide chain and the carbohydrate moiety. The stack has polarity, with the cis-side adjacent to the reticulum and the other, trans-side, oriented towards the secretory granules or the centriole. Regulation at the transcriptional level occurs according to the functional state of the cell, and the immunoglobulins synthesized possess either a hydrophobic segment allowing insertion into the membrane, or a hydrophilic region which marks them out for secretion.