Proteins are the fundamental building blocks of life. They form high performance materials and carry out cellular functions. They are able to fulfil these roles by assembling together to form sophisticated structures and architectures, which in many cases extend to mesoscopic liquid or solid phases. This talk focuses on understanding the transitions between these phases, their fundamental material properties and the way that the modulate biological function and malfunction. I will then discuss two applications opened up by the control of protein assembly and show how this approach can lead to the generation of new types of sustainable materials assembled from natural building blocks, as well as the discovery of molecules that can ameliorate malfunctioning protein self-assembly in a range of age-associated disease states.