Binary nanocrystal superlattices (BNSLs) emerge as an important class of man-made materials where components and functionalities can be added, tuned, or combined in a predictable manner. These amazingly complex structures spontaneously self-assemble from colloidal solutions containing binary mixtures of functional (semiconducting, magnetic, plasmonic, etc.) nanocrystals. Further developments of the BNSL-based materials require a deep understanding and control over BNSL formation and structural perfection. Like any solid, BNSL can contain different kinds of structural defects. It is well-known that defects can have a tremendous effect on the material's behavior. Defect engineering is used to modify and improve many of the mechanical, electrical, magnetic, and optical properties of conventional solids. In this work, we provide the first systematic analysis of structural defects in various BNSL structures. We used BNSLs as a platform for studying structural defects in both periodic (crystalline) and aperiodic (quasicrystalline) lattices, as well as for direct imaging of the interfaces between crystalline and quasicrystalline domains. Such direct observation of local imperfections in complex multicomponent lattices provides a unique insight into the fundamental aspects of crystal formation.