Robust inferences about the interior require self-consistent descriptions of bulk physical properties in terms of radial reference Earth models and lateral heterogeneity in terms of three-dimensional tomographic models. These complementary aspects of seismic imaging are typically considered in isolation since radial and tomographic models often employ divergent modeling approximations, discrepant observations and starting models. Full-spectrum tomography permits global tomographic models whose average structure is constrained using the sensitivity afforded by normal-mode eigenfrequencies, Earth's mass and moment of inertia. Additional constraints on both radial and lateral variations are afforded by a large and diverse set of observations comprising free-air gravity anomalies, surface-wave phase anomalies, body-wave travel times, normal-mode splitting functions and long-period waveforms. Below are the reference Earth models while a growing set of models derived using this modeling philosophy are available elsewhere.