Starch synthases, EC 2.4.1.21, are the plant enzymes that build starch: they transfer the glucose moiety from ADP-glucose to glucose-containing polysaccharides by means of alpha-1,4 linkages. The entry also covers glycogen synthases that utilize ADP-glucose. Plant tissues contain several isoforms that build starch, assembling amylose and amylopectin together within the granule. They are studied in crop science and plant biochemistry because their activity shapes starch yield, granule structure, and ultimately the functional properties that millers, bakers, and processors rely on.