The functional roles of plant biopolymers range from carrying genetic information; structural integrity; storage of carbon, nitrogen, and other elements; energy storage; defense against pathogens; and desiccation. Several such biopolymers, especially the abundant energy storage or structural compounds, are easily prepared in bulk, and their properties make them useful as food- and feedstocks, as materials, and as energy carriers. With decreased availability of petroleum and the negative carbon footprint associated with its use, biomaterials are considered attractive substitutes for petrochemical-based materials, such as plastics and elastomers. In this chapter, the focus is on biomaterials derived from natural plant polymers, such as starch, cellulose, rubber, and proteins, as well as on novel polymers produced in transgenic plants, such as polyhydroxyalkanoates, fibrous proteins, and poly-amino acids. Also discussed are the scientific, technical, and societal bottlenecks that must be considered in order to establish priorities and ensure the viability of producing biomaterials from plants.