A wide range of quantum atom-light interfaces are currently under development which challenge our traditional quantum optical theories and necessitate new approaches. These platforms range from dense atomic media either in the form of ordered arrays or disordered ensembles, to nanophotonic ``crystals'' made of atoms and light, to quantum electrodynamical circuits coupled to superconducting qubits. Common features of such systems are the capability to strongly alter the dispersion relation of light (e.g., the formation of optical band gaps or topological bands), the ability to reduce the dimensionality or create completely synthetic geometries in which photons and matter interact, and/or the enhancement of multiple scattering phenomena to the point that they become non-perturbative. The need to account for this additional complexity results in a class of new models for atoms interacting with light, which typically resemble many-body quantum ``spin'' models featuring out-of-equilibrium driving, and long-range coherent and collective dissipative interactions.

This program will gather together scientists with diverse backgrounds in order to better pose the grand challenges and opportunities in this field, put forward creative approaches to tackle this new many-body problem, develop powerful new protocols for quantum science applications, and search for exotic phenomena that cannot exist even in principle within previous theories. The program strives to significantly re-shape the field of quantum light-matter interactions and re-define the boundaries of what is physically and technologically possible with atoms and light.