The study of protein-based materials has enabled the development of several optical, electronic, and medical technologies. Within this context, cephalopod (e.g., squid, octopus, cuttlefish) structural proteins called reflectins have recently gained attention due to their demonstrated potential for the development of biophotonic and bioelectronic devices. Moreover, reflectins make up the subcellular structures found in optically active cephalopod skin cells that play a critical role in cephalopods’ remarkable camouflage abilities. Given reflectins’ significance from both fundamental biology and materials science perspectives, these proteins have recently emerged as a desirable target for the design of functional biomaterials. However, despite their interesting optical (e.g., high refractive index) and electrical (e.g., excellent proton conductivity) properties, the development of reflectin-based materials has been hindered by a lack of complete understanding of the relationships between their structures and properties. Moreover, an incomplete understanding of such relationships also limits our grasp over the exact mechanisms by which reflectins enable cephalopods’ optical functionalities. This dissertation discusses the investigation of the structure-function relationships of reflectin proteins. Specifically, the dissertation focuses on the (a) elucidation of the molecular structure of a model reflectin variant, (b) development of a straightforward strategy for precisely controlling the structure, self-assembly, and optical properties of the model reflectin variant, (c) investigation of the self-assembly and optical properties of a full-length reflectin isoform, (d) interrogation of the aggregated-state structural characteristics and electrical properties of the model reflectin variant, and (e) validation of new processing strategies such as inkjet printing for the fabrication of conductive reflectin films. This work not only sheds new light on the role of reflectins in cephalopod structural coloration but also lays the foundation for the development of novel reflectin-based materials for biophotonic and bioelectronic applications.