<p>Some of the highest-performance materials in nature, including spider silk and collagen, are formed through protein self-assembly. These natural materials, which combine function, performance and assembly under mild aqueous conditions, have inspired a generation of technologically useful biomaterials that use natural proteins as the molecular building blocks. The shift from oil-based feedstocks towards renewable materials has accelerated the search for plastic replacements and has stimulated work in the two major classes of abundant natural polymers, proteins and polysaccharides. Whereas polysaccharides are already used in areas from packaging to structural applications, the unique properties of proteins have not yet been fully harnessed for renewable materials. Advances over the past 15 years have highlighted the promise of protein systems for high-performance applications, enabled by a fundamental understanding of polypeptide self-assembly, emerging computational methods such as artificial intelligence, feedstocks, and materials processing. In this Review, we highlight developments in this area and provide a perspective on the potential of this important class of molecules in both fundamental materials science and sustainability.</p>