Quantum Mechanics and Gravity describes a paradigm change in modern physics from the philosophy and mathematical expression of the quantum theory to those of general relativity. This approach applies to all domains - from elementary particles to cosmology; the change is from the positivistic views in which atomism, nondeterminism and measurement are fundamental, to a holistic view in realism, in which matter - electrons, galaxies - are correlated modes of a single continuum, the universe. It explicitly defines the field that unifies electromagnetism, gravity and inertia, with new predictions, in terms of quaternion and spinor field equations in a curved spacetime. This unified field theory is derived from first principles in the sense of Einstein's continuum field theory in general relativity, in contrast with the attempted unification in the context of the quantum theory (called the "Grand Unified Theory" - GUT). Quantum mechanics emerges as a linear, flatspace approximation for the equations of inertia in general relativity.