This chapter describes the composition and metabolism of carbohydrates. Carbohydrates include a large group of compounds commonly known as starches or sugars, widely distributed in plants and animals. Chemically, they are described as polyhydric alcohols, having potentially active aldehyde and ketone groups. In general, carbohydrates are white solids, freely soluble in water with the exception of certain polysaccharides. Carbohydrates of lower molecular weight have a sweet taste. This chapter covers the types, structure, composition and uses of carbohydrate, monosaccharides, disaccharides, polysaccharides and oligosaccharides, digestion and absorption of carbohydrates, carbohydrate metabolism, glycolysis, glycogenesis, cori cycle, pentose phosphate pathway, citric acid cycle, glycogenolysis, regulation of blood sugar level, blood glucose monitoring, glucose tolerance test (GTT), Barfoed’s Test, Benedict’s test, diabetes mellitus, glycogen storages diseases, galactosemia, hereditary fructose intolerance, and disorders of pyruvate metabolism.