The higher-order structure (HOS) of a protein (secondary, tertiary, and quaternary structure) is important for proper biological function. Analytically measuring the HOS properties of a biotherapeutic and understanding the relationships between structure and function are important, because they directly influence a drug's efficacy and safety. This article looks at how hydrogen-deuterium exchange mass spectrometry (HDX-MS), an MS-based labelling approach, has begun to serve as a means for performing routine biophysical analysis.