We explore the impact of sub-wavelength structural control on optical dispersion, optical forces, and optical nonlinearity in nanophotonic systems. Through a general exploration of both Raman and Brillouin interactions, the physics of photon phonon coupling will be explored over a range of length-scales and time-scales. First, THz frequency photon-phonon coupling, through stimulated Raman scattering, will be discussed. We show that the complex dynamics produced by Raman scattering can be harnessed to create wavelength agnostic laser sources spanning mid-IR wavelengths. Additionally, through a fundamental examination of energy and force, we show that optical forces in nanostructured systems radically change the nature of nonlinear interactions. For instance, strong light-boundary interactions yield new forms of Brillouin nonlinearity that produce tailorable coherent phonon emission in nanophotonic systems. Exploiting these strong light-matter interactions, we demonstrate stimulated Brillouin scattering in silicon waveguides for the first time, yielding radically enhanced and tailorable third order nonlinearities.