Recent reviews discuss the experimental methods that provide structural information on multiple conformational states of biomolecules . Crystallographic studies, using either X-ray or neutron diffraction, may capture different states in different crystal forms. Electron density can also often be fit to multiple conformations within a single crystal. Room-temperature (or higher temperature) X-ray crystallography may avoid structural bias from cryogenic cooling and reveal motions crucial for catalysis, ligand binding, and allosteric regulation . Other experimental data types, such as small-angle Xray scattering (SAXS) and electron microscopy (cryoEM) data, can frequently only be fit to multi-conformer models. Additionally, Förster resonance energy transfer (FRET), Double Electron-Electron Resonance (DEER) spectroscopy, and chemical cross-linking data have been used to model multiple conformational states since they can characterize interprobe distance distributions . With all experimental data, multiple-state fitting may be indicated and (cross)-validated only when a single-state model is inadequate.