Many-body physics with photons and polaritons is a highly interdisciplinary field, merging diverse areas such as nano-photonics, quantum optics, condensed matter physics, and quantum technologies. The inherent accessibility to local observables, and the ability to probe out-of-equilibrium phenomena make driven many-body photonic systems especially promising for a variety of applications in quantum simulations and quantum computing, as well as in materials science and optical circuitry.