Cellulose and starch represent two of the most ubiquitous and versatile polysaccharides. Their applications include uses in packaging, biomedical applications, electronics, agriculture, and many other areas at the forefront of exploration for reducing dependency on nonrenewable fossil resources. Starch, unlike cellulose, is much more readily solubilized or dispersed in aqueous solutions. However, the development of green solvents including ionic liquids and deep eutectic solvents has improved accessibility for derivatization of these biopolymers. Degradation mechanisms via acid or enzymatic hydrolysis have been explored to produce biofuels including ethanol. To take advantage of the unique properties of their derivatives, the functionalization and formulation of cellulose and starch have been investigated in composite materials, blends, dispersions, and hydrogels, spanning various sustainable and commercially relevant applications.