In 2030, 200-million tons of co-product lignins could emanate from biorefineries converting lignocellulose to liquid fuels and organic chemicals. Reliable design of lignin-based plastics is only achievable when the physicochemical behavior of the constituent polymers has been correctly understood. Originally, the hydrodynamic compactness of lignin derivatives at the macromolecular level was thought to arise from crosslinking. Now it is recognized that the noncovalent forces between aromatic moieties in lignin components are very strong. Recently, it became apparent that, by simple physicochemical means, most of the lignins in wood meal can be separated into well-defined fractions with different frequencies of macromolecular substructures. Last year, a detailed mechanism was proposed for the final step in lignin biosynthesis as the means through which the configurations of lignin domains are established in muro. The cogent design of lignin-based plastics rests on both the primary structures of lignin chains and the intermolecular interactions between them.