The structural versatility of metal-oxo cluster chemistry, in combination with the option of deliberate utilization of well-defined building blocks, serves as the foundation for the generation of a library of functional molecular moieties. The development of appropriate synthetic strategies and approaches as well as analytical techniques allows us in this chapter to highlight the domains of the fundamental structure research on the oxo clusters of transition, main group, and lanthanide metals. An abundance of structural investigations endows them with consecutive exploration of great prospects in applied areas as diverse as catalysis, magnetism, nanotechnology, and material science due to their intrinsic features such as structural tunability and robustness as well as thermal and redox stability.