Bionanoparticles offer both intra- and inter-molecular self-assembly. Obviously, when considering protein-based particles/structures, intramolecular self-assembly is eminently suitable to obtain the specific three-dimensional structure. This three-dimensional structure offers the possibility of forming larger assemblies because the three-dimensional structure offers specific interparticle interactions that drive the formation of large fiber-like structures as encountered both in the intracellular matrix, e.g. microtubules and actin microfilaments, and in the extracellular matrix, e.g. collagen, elastin and fibronectin. Additionally, there are protein-based structures that assemble into a defined nanosized structure, which were originally used in Nature for storage, such as ferritin, but also complex architectures, such as viruses, that are a common occurrence. All these structures can be utilized for functional structures in, e.g., biomaterials science and bioelectronics, as drug delivery platforms and many more. Although proteins with aggregation properties are useful in the aforementioned applications, interprotein aggregation also lies at the foundation of many neurodegenerative diseases. This usually is a result of a compromised three-dimensional structure where (partial) unfolding results in aggregation (amyloid formation) and a correct and stable intramolecular assembly is required. This chapter considers intra- and intermolecular assemblies of proteins that offer functional bionanoparticle-based structures and assemblies. As important specific structures, ferritin, collagen and virus particles are discussed.