<p>The emission of electromagnetic waves from solids encompasses a wide range of processes, including incandescence, fluorescence, electroluminescence, scintillation, cathodoluminescence and light emission from inelastic tunnelling. Different models can be used to describe them; for example, thermal emission from hot bodies is computed using statistical physics, photon emission from an excited electron is treated with quantum mechanics and emission from a current in an antenna is quantitatively described by Maxwell’s equations. However, most emitting systems involve statistical ensembles of excited electrons interacting with complex electromagnetic environments, so a blend of the three approaches is needed. The purpose of this Review is to provide a unified framework that combines recent theoretical works that have been developed to quantitatively account for light emission processes in solids. We begin with an overview of the electrodynamics approach used to model incandescence. This framework is then extended to describe light emission from optically or electrically pumped semiconductors. Finally, we generalize the procedure to strongly non-equilibrium systems and illustrate its application through several examples.</p>