Publisher Summary This chapter explains nonstarch polysaccharides (NSPs), which are the major part of dietary fiber (DF) and includes cellulose, pectins, glucans, gums, mucilages, inulin, and chitin. NSPs are the principal components of the plant cell wall and constitute a major source of fiber in the diet. They are classified into soluble and insoluble fractions. The insoluble fraction of NSP is normally found on the outer protective layer of plants, whereas soluble NSP is normally found in the inner parts of plants The key aspect of NSPs is that they are plant materials that are not digested by the enzymes of the human digestive tract but remain fermentable in the large intestine. NSPs are the principal components of dietary fiber and the lack of small intestinal digestibility explains the majority of their principal physiological properties. The physicochemical properties of NSPs result in a number of physiological effects that are related to certain health benefits. They are claimed to modulate blood glucose and insulin responses to foods to lower blood cholesterol and to have beneficial effects on the prevention and treatment of certain diseases like gallstones, diverticular disease, obesity, constipation, or colon cancer.