Photosynthetic plants produce a wide range of glycan compounds [1]. These include cell wall polysaccharides involved in cell development and morphogenesis [2], glycoproteins and glycolipids involved in various cell functions, and glycoside of specialized metabolites involved in stress responses and environmental adaptation [3]. The production of diverse glycan compounds by plants is related to the large number of carbohydrate-related enzyme genes encoded in the plant genome (more than twice that of the human genome) [4]. For many plant glycan compounds, the genes of enzymes involved in their synthesis and degradation are yet to be identified, and their functions remain unknown [5]. Plant glycan compounds are deeply involved in human life, not only in clothing, food, and housing but also as energy sources (Fig. 46.1). Recent study has begun to identify glycan compounds that contribute to human health. Food starch is often used as a material for biofuels. This raw material is expected to replace lignocellulose, which is not a food source, but its use is currently limited.