At present the ability to control the properties of polymeric materials through manipulation of microstructure is limited due to synthetic procedures that usually afford materials with considerable heterogeneity of molecular architecture. Although conventional polymer synthesis has enabled the preparation of wide variety of materials for diverse technological applications, the next generation of advanced materials will likely encompass design concepts from natural systems, such as tissues and bone, in which complex hierarchical structures are synthesized with very high specificity. Emulation of these natural systems requires the precise specification of intermolecular interactions between materials components, which necessitates the near-absolute control of molecular structure that is currently inaccessible via conventional materials synthesis. However, protein-based materials can be synthesized with near absolute uniformity of macromolecular architecture using in vivo biosynthesis, and may be considered model uniform polymers capable of forming hierarchically ordered systems with multiple levels of interactive structure. By utilizing the principles of protein structure and the concepts of polymer materials science, non-natural protein-based polymers can be designed that are capable of being elaborated into materials targets with unique properties that arise as a consequence of their structural specificity (Scheme 1). Novel methods for the facile construction of concatameric genes that encode precisely defined, repeating peptide blocks have been developed,1 which have enabled the preparation of protein polymers with near-absolute control of size, composition, sequence, and stereochemistry. Using this approach, protein polymers have been designed on the basis of structural features programmed into the polypeptide at the molecular level that self-assemble into lamellar crystallites,2 lyotropic smectic mesophases,3 and thermo-reversible nanoparticles.4 Study of these materials is essential for understanding the elements of structure-based design in materials research, but the design principles elucidated in these studies may have potential for applications in medicine and nanotechnology.