This article presents a review of techniques and instrumentation for using x rays and synchrotron radiation in high-pressure experiments. The review focuses on x-ray diffraction experiments using diamond anvil cells. After a brief introductory passage, details about diamond anvil cells, large volume apparatus, pressure measurement, and simultaneous high-temperature and high-pressure instrumentation are provided, with adequate references to these topics. A section on adapting x-ray methods for use with high-pressure apparatus lists the problems encountered. Examples of studies are presented using energy dispersive diffraction, angle dispersive diffraction, infrared spectroscopy, x-ray absorption spectroscopy, and single-crystal techniques. The current trend indicates that energy dispersive diffraction, so far the mainstay of high-pressure powder diffraction with synchrotron sources, has lost some ground to angle dispersive diffraction, due to advances in instrumentation in the latter method. ©1997 American Institute of Physics.