Cellulose, a polysaccharide consisting of numerous β-glucose units joined by glycosidic bonds, is the main constituent of plant cell walls and is the most abundant organic polymer on earth. It is insoluble in water or common organic solvents since it is highly crystalline and aggregates strongly via hydrogen bonding. It is thus difficult to separate from plants, and cannot be melt-processed. However, cellulose may be derivatized into esters or ethers, the most widely reported being cellulose acetate (CA), cellulose propionate (CP), and cellulose acetobutyrate (CAB), then isolated and processed into various forms of plastics. For instance, cellulose acetate, with its good clarity, toughness and processability, had been used as a film stock since 1934 before being replaced by polyester films in the 1980s. It still has wide applications today including optical films and food or drug packaging. A recent study shed a new light on cellulose acetate's biodegradability and revealed that it disintegrates in seawater in just months, much faster than previously believed. An alternative method to isolate cellulose is by dissolving it with some uncommonly used solvents containing various bases or salts, then casting into films or spinning into fibers, resulting in what is known as regenerated cellulose. Research on various solvents, such as carbon disulfide, N-methylmorpholine-N-oxide, dimethylsulfoxide, and urea, have been reported; green solvents such as ionic liquids have recently been proposed to address environmental concerns. Like starch, cellulose and derivatives are used more often as fillers or reinforcing fibers for other polymers, rather than as plastics themselves.