Bafia, D. JACoW Publishing Geneva, Switzerland Bulk niobium SRF cavities remain as a leading technology in the realization of the next generation of particle accelerators and serve as the highest Q₀ platform for 3-D quantum computing architectures. Whether utilized in kilometer long accelerators or 10 cm long quantum processors, the performance of these cavities is largely determined by the material properties within the 100 nm from the inner RF surface. This talk will discuss advancements made in the development and understanding of surface engineering techniques (doping with O or N, N-infusion, and low/mid temperature baking) on niobium SRF cavities in different regimes: mK and single photon levels for quantum computing and high Q/high G accelerator applications. By coupling material science and resonator measurements, we delineate the role of different impurities in enabling excellent performance in each of these regimes.