Polysaccharides are polymers, almost unique to the plant kingdom, with either energy storage or structural roles that are both relevant to human food. Starch provides energy storage in plants and makes a major contribution to the energy content of human diets, notably cereals. Starch's behaviour, in bread making etc. (including staling) and as a thickener, is dependent on its molecular structure and organisation in granules. Chemical modification of starch provides valuable food additives. Amylases etc. are used to manufacture pure glucose and other products. Pectins, complex polymers of galacturonic and other monosaccharides, notably rhamnose, contribute to the characteristics of preserves etc. The seaweed polysaccharides, alginates, carrageenans etc. have gelling and thickening properties that are widely exploited in food products and have been the key to understanding gel structure. Cellulose and hemicelluloses are important in human diets as dietary fibre with benefits for bowel function, cholesterol metabolism and glycaemic index. Gums, highly branched polymers of various monosaccharides, are valued as thickening and gelling agents. The chapter includes a detailed listing of the polysaccharides permitted as food additives in the EU, USA and elsewhere and concludes with a list of specialist books and review articles for further study.