Polysaccharides derived from plant cell wall materials play an important role in our diet. Dietary fibers work as prebiotics in the human gut, and some plant polysaccharides are known to have more direct beneficial impacts on human health. In the food industry, plant fiber materials, such as gums are widely used as structural ingredients. Complex polysaccharides account for most of the plant cell wall, and their biosynthetic pathways and their regulation are largely unknown. Systematic collaborative efforts for defining the structure and impact on human health of beneficial fibers and elucidating the biosynthetic pathways and their regulation will open a great potential for biotechnological applications.