Typically, photons interact only weakly with themselves and other particles. For instance, a photon crossing Earth's atmosphere has only a 50% chance of being scattered. Cavity Quantum Electrodynamics (CQED) explores the physical consequences of the opposite extreme. It is a platform for studying light-matter interactions at the single photon, single atom level. Resonant effects enhance the dynamics in such systems. In Paris, CQED involves a Fabry-Perot type cavity resonator that confines single photons, via standing-wave reflections, in proximity to large-dipole atoms in free space. This setup allows experimentalists to probe quantum mechanics directly. Some of the first precision measurements of single-particle quantum dynamics were demonstrated in CQED-type experiments. These ideas were adapted to superconducting circuits, in circuit QED (cQED), where transmission line resonators and artificial atoms are coupled in analogous ways. Because the atoms in cQED are designable, significantly stronger coupling is achievable for cQED, allowing new regimes of light-matter interaction to be explored. A recent evolution blurs the line between the fields of cQED and CQED, integrating artificial atoms directly with superconducting cavity resonators. The result is a more coherent circuit and a more cooperative quantum coupling. The cavity's higher coherence is a resource for the more-dissipative artificial atom, while the atom's large nonlinearity allows for high-fidelity control over the photonic state in the cavity resonator. Schemes for using cavities as quantum memories may allow for fundamental tests of quantum error correction and challenge the common frameworks of universal quantum computation.