Starch is a fundamental polysaccharide widely distributed in amylaceous biomasses such as corn, cassava, potato, wheat, and rice. This chapter explores the structural, biochemical, and technological aspects of starch, emphasizing its role in food, bioenergy, and industrial applications. This chapter describes the biosynthesis of amylose and amylopectin, the diversity of starch granules, and the influence of environmental and genetic factors on starch composition. Extraction and purification methods are discussed, along with physical, chemical, enzymatic, and genetic modification techniques that enhance starch functionality. Economic aspects, including global production, trade policies, and cost structures, are analyzed in light of the growing demand for starch in bioplastics and biofuels. Special attention is given to innovative, sustainable processes that align with circular bioeconomy principles. This chapter also highlights the role of starch in biorefineries and its potential in emerging applications such as ethanol-to-jet (ETJ) fuels and biodegradable materials. By integrating scientific, technological, and economic perspectives, this work offers a comprehensive framework for understanding and advancing the use of amylaceous biomasses in sustainable development.