The interface between Quantum Theory and theories of gravity, including General Relativity, is still poorly understood. Even the consistent coupling of genuine quantum systems to classical gravitational fields show novel features that we are only beginning to understand, leaving alone the problem of Quantum Gravity proper. In this RT we aim to clarify certain well defined issues by means of concrete models, concerning semi-classical self-gravitating quantum systems as well as phenomenological models for quantum-gravity induced symmetry reductions or symmetry deformations.