The last decades have witnessed an unprecedented surge in the study of matter and materials at extreme values of pressure and/or temperature. The fundamental importance of this research stems from the fact that high pressure can deeply modify chemical bonds and induce myriad changes in materials. Many breakthroughs have been achieved at synchrotrons worldwide, in fields ranging from earth and planetary sciences to fundamental physics, chemistry, and materials research, and even in the life sciences, where questions on life and biological function under extreme conditions have been studied.