This review summarizes fifty years of carbohydrate chemistry, from studies of reaction mechanisms and development of synthetic methods to the design of specific compounds for investigations of cancer glycoproteins. Through these years of intensive research, many carbohydrate derivatives were shown to be biologically relevant, for example the fragments of bacterial polysaccharides and imino sugars that were potent inhibitors of glycosidases. Oligosaccharides and O- glycopeptides with GalNAc-Ser/Thr linkages were essential for studies of cancer immunology and the specificities and inhibition of cancer glycosyltransferases. Thus carbohydrate chemistry has provided the basis for our knowledge of the biochemistry and immunology of cancer cell glycoproteins.