There are many different ways to generate light, but they all involve electric charges moving about. When these charges accelerate, then a simple law of physics is that they emit light. Understanding this was one of the great achievements of the theory of electromagnetism. ‘Light matters’ considers different methods of generating light, from heating material, as in an ordinary light bulb where an electric current is passed through a metal filament, to synchrotron radiation, which generates X-rays. It also explains quantum light emission processes and coherence, and goes on to describe laser light (perhaps the most important invention in optics in the last century), X-rays, and ultrashort light pulses.