The area of nanotechnology is progressing quickly, with active nanoparticles and nanomaterials playing critical roles in many different fields, including as environmental remediation, energy, and healthcare. The following section offers a thorough introduction related to the fundamental concepts and advanced methodologies utilized to determine the chemical, physical, structural, and functional aspects of active nanoparticles and nanomaterials. The focus is on linking structural features to functional performance, which will guide the logical design of nanomaterials for specific applications. The chapter also tackles the issues of repeatability, scalability, and standardization in nanoparticles characterization, as well as future trends and advances in the field.