qMRI is a rapidly evolving scientific field of high current interest because it has the potential of radically changing the clinical and research practices of magnetic resonance imaging (MRI). This title focuses solely on the theoretical aspects of qMRI, which are treated and analyzed at three different spatial scales, specifically: the quantum physics scale of individual spins; the semi-classical physics scale of spin packets; and, the imaging scale of voxels. Topics are presented paying particular attention to theoretical unification and mathematical uniformity.