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Rapid growth of plasmonics and nonlinear optics in recent decades has driven a new demand for materials having simultaneously large optical responses and excellent robustness to extreme environments. Adding to this challenge, useful applications of plasmonic and nonlinear optical devices for nanophotonics require that not only the previous criteria be met, but highly controllable materials fabrication over minute length scales must be achievable as well. These increasingly stringent requirements can be met with low loss metallic nanofilms and nanocomposites of some noble metals like Ag and Au, and some alternative plasmonic materials such as transition metal mononitrides (TMNs) like TiN and ZrN. Desire for the attainment of new plasmonic devices with low losses and large nonlinear responses has shifted interest into the quantum-size regime. This dissertation explores means of manipulating the chemistry, defects, geometry, and dimensionality of these quantum-size metals in order to achieve materials with desirable, tunable properties. In these explorations, optical, structural, and chemical characterizations are jointly employed with advanced fabrication techniques to innovate and optimize new materials, and to fill in contemporary and technologically-important gaps. Pushing the physically-fabricable limits of the quantum materials and the limits of their crystalline order is the transdimensional regime where film properties are massively tunable with small changes to a film's minute thickness. Passing some kinetic limitations on the fabrication of quantum-size Au films, TMNs can be grown down to the atomic scale and not only their crystal structures but their dimensionality as well can be controlled with choice of growth conditions, substrate, and environment. The investigations given in this dissertation represent efforts to push the boundaries of what real materials can do by combining simulation and experimentation to predict and demonstrate how optical properties in metallic nano- and quantum-sized materials can be tuned with asymmetric structuring, dimensionality, chemistry, defect engineering, and chemistry. The nano- and quantum-sized metals realized in this work reduce barriers to attaining gigantic, efficient, and low-loss light-matter interactions and present new means of achieving such.