Well‐Defined Nanostructures: Concept, Impact and Perspective

Abstract Well‐defined nanostructures (WDNSs) represent a transformative frontier in nanotechnology, enabling precise control over material properties through nanoscale engineering. The connectivity of nanoscale building blocks is increasingly critical in defining the properties and applications of WDNSs. Traditional dimensionality‐based classifications provide foundational insights but overlook the delicate influence of connectivity architectures on functionality. This perspective introduces a supplementary classification framework based on connectivity modes, including discrete connections, serial connections, 2.5D connections, and 3D interpenetrations. Each category defines specific structural configurations that decide the spatial arrangement, interaction dynamics, and functional integration of nanoscale components. This framework establishes a unique perspective for understanding WDNSs, linking their structural design with diverse applications in catalysis, energy storage, biomedicine, and beyond. By regulating connectivity strategies with emerging functional demands, WDNSs offer considerable opportunities for designing multifunctional materials, providing a foundation for advancing nanotechnology in addressing complex scientific and societal challenges. Finally, advanced rational design, accurate synthesis, comprehensive deployment, and sustainable development remain critical to addressing bottlenecks in WDNSs development.