The dynamic response of magnetic materials lacks time-reversal symmetry and can often be described through the propagation and evolution of waves of magnetic orientation, or spin waves. These spin waves, or magnons when quantized, can move without electric charge motion, yet spin-orbit interactions allow the spin waves to couple, sometimes very strongly, both to voltages and to illumination. I will describe progress over the last several years in calculating and understanding, in collaboration with experimentalists, the coupling of magnons to microwave and optical photons as well as the manipulation of spin-wave propagation with a voltage. In analogy with optomechanics, two photons will interact, within a cavity containing a ferrite, with a magnon mode to coherently modify the spontaneous emission rate, to exhibit electromagnetically-induced transparency and even to reach the strongly-coupled quantum regime. Patterned magnetic media can also amplify voltage-dependent effects to produce voltage-tunable oscillators or filters.