This thesis offers a systematic investigation of reference frames in General Relativity, with a particular emphasis on distinguishing them from coordinate systems. A novel classification of reference frames is proposed, grounded in their dynamical coupling to the gravitational field. Building on this classification, the dissertation revisits Earman’s symmetry principles, demonstrating that relaxing the assumption of dynamical coupling gives rise to a novel violation of the SP1 principle. The notions of influence and correlation between fields are analysed, enabling a principled distinction between physical and dynamical fields. The thesis also addresses the concept of observability in General Relativity, criticising existing notions in the relevant literature and advancing a new interpretation of Einstein’s point-coincidence argument, with implications for the ontology of spacetime.