Recent advances in studies on plant ADP-glucose pyrophosphorylase (AGP), the key enzyme of starch biosynthesis, are presented. AGP constitutes the first committed and highly regulated step of starch synthesis in all plant tissues. The importance of AGP in carbohydrate metabolism and several of its features, such as potent regulation by cellular effectors (3-phosphoglycerate and Pi), an unusual two subunit-types structure, tissue-specific and developmentally-regulated expression, and presence of the AGP-deficient mutants, make it an attractive, but complex, target for biotechnological manipulations. Some strategies for future research on AGP are discussed.