  Cavity magnonics deals with the interaction of magnons - elementary
excitations in magnetic materials - and confined electromagnetic fields. We
introduce the basic physics and review the experimental and theoretical
progress of this young field that is gearing up for integration in future
quantum technologies. Much of its appeal is derived from the strong
magnon-photon coupling and the easily-reached nonlinear regime in microwave
cavities. The interaction of magnons with light as detected by Brillouin light
scattering is enhanced in magnetic optical resonators, which can be employed to
manipulate magnon distributions. The cavity photon-mediated coupling of a
magnon mode to a superconducting qubit enables measurements in the single
magnon limit.
