Cardiac magnetic resonance (CMR) relaxometry (including T2*, T1 and T2 mapping, as well as extracellular volume (ECV) assessment) has emerged as an accurate, reproducible, highly sensitive, and quantitative technique for characterizing diffuse myocardial processes underlying cardiac diseases. This presentation will build upon the physics of relaxometry - showing not only the biologic value of these novel CMR techniques, but their practical clinical utility in the care of patients with myocardial pathology. From hypertrophic cardiomyopathy and Duchenne muscular dystrophy to iron overload cardiomyopathy, cardiac transplant rejection and more, relaxometry is changing the way clinicians think about patient care.