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Treating reference frames fundamentally as quantum systems is inevitable inquantum gravity and also in quantum foundations once considering laboratoriesas physical systems. Both fields thereby face the question of how to describephysics relative to quantum reference systems and how the descriptions relativeto different such choices are related. Here, we exploit a fruitful interplay ofideas from both fields to begin developing a unifying approach totransformations among quantum reference systems that ultimately aims atencompassing both quantum and gravitational physics. In particular, using agravity inspired symmetry principle, which enforces physical observables to berelational and leads to an inherent redundancy in the description, we develop aperspective-neutral structure, which contains all frame perspectives at onceand via which they are changed. We show that taking the perspective of aspecific frame amounts to a fixing of the symmetry related redundancies in boththe classical and quantum theory and that changing perspective corresponds to asymmetry transformation. We implement this using the language of constrainedsystems, which naturally encodes symmetries. Within a simple one-dimensionalmodel, we recover some of the quantum frame transformations ofarXiv:1712.07207, embedding them in a perspective-neutral framework. Usingthem, we illustrate how entanglement and classicality of an observed systemdepend on the quantum frame perspective. Our operational language also inspiresa new interpretation of Dirac and reduced quantized theories within our modelas perspective-neutral and perspectival quantum theories, respectively, andreveals the explicit link between them. In this light, we suggest a new take onthe relation between a `quantum general covariance' and the diffeomorphismsymmetry in quantum gravity.

A change of perspective: switching quantum reference frames via a perspective-neutral framework