High-pressure methods for solving protein structures by X-ray crystallography and NMR are maturing. These techniques are beginning to impact our understanding of thermodynamic and structural features that define not only the protein's native conformation, but also the higher free energy conformations. The ability of high-pressure methods to visualize these mostly unexplored conformations provides new insight into protein function and dynamics. In this review, we begin with a historical discussion of high-pressure structural studies, with an eye toward early results that paved the way to mapping the multiple conformations of proteins. This is followed by an examination of several recent studies that emphasize different strengths and uses of high-pressure structural studies, ranging from basic thermodynamics to the suggestion of high-pressure structural methods as a tool for protein engineering. © 2011 by Annual Reviews. All rights reserved.