Using a new class of optomechanical waveguides that produce large Brillouin nonlinearities, we realize Brillouin lasers, Brillouin amplifiers, and Brillouin-based signal processing technologies in silicon photonics. Counterintuitively, the same nanophotonic silicon waveguides that greatly enhance both Kerr and Raman nonlinearities exhibit vanishingly small Brillouin nonlinearities. Only with the advent of new optomechanical waveguides-that guide both light and sound-have Brillouin interactions been transformed into the strongest and most tailorable nonlinearities in silicon. We summarize progress in the rapidly growing field of integrated Brillouin photonics, and explain how a variety of simulated lightscattering processes can be engineered to (1) create Brillouin-based optical amplifiers, (2) tailor optical susceptibility, and (3) create new signal processing technologies in silicon photonics. Finally, we harness Brillouin-based opticalamplification to create the first silicon-based Brillouin lasers and we discuss their performance characteristics.