Nanophotonic engineering offers powerful methods of tailoring light-matter interactions. By manipulating optical environments at the nanoscale, we can influence the rate, direction, and spectral distribution of optical emission. This thesis describes the foundations of nanophotonic engineering and discusses methods to tailor the optical response of solid-state quantum materials. We target color centers in diamond membranes and two-dimensional semiconductors, two classes of optical emitters that offer applications in quantum information processing, sensing, and integrated optoelectronics. Throughout this work, we emphasize the development of nanofabrication processes which are compatible with these materials and enable sub-wavelength control of their optical environments. Chapter 1 introduces the fundamentals of nanophotonic engineering and provides background on the material systems explored in this work. Chapter 2 describes the benchtop optical experimental methods that enable many of the measurements presented later. Following these introductory chapters, Chapter 3 details our approach to fabricating integrated photonics using templated atomic layer deposition of TiO2. Chapter 4 presents work that leverages this nanofabrication process to integrate photonic devices with a range of quantum materials. Chapter 5 extends this approach to a novel device geometry, multi-resonant bullseye antennas. In Chapter 6, we discuss the application of off-resonant planar cavities to extend the lifetimes of optical excitations in two-dimensional semiconductors. Finally, Chapter 7 provides a summary and outlook for this work.