Vibrational Spectroscopy at High External Pressures: The Diamond Anvil Cell presents the effects of high pressure on the vibrational properties of materials as accomplished in a diamond anvil cell (DAC). The DAC serves the dual purpose of generating the pressures and being transparent to infrared radiation, allowing the observation of changes caused by pressure. The optical probes highlighted will deal principally with infrared and Raman scattering, although some observations in the visible region will also be presented. The book begins with a discussion of the effects of pressure and pressure units. This is followed by separate chapters on the instrumentation needed to study vibrational transitions under pressure and pressure calibration and various methods used to measure pressure in the DAC. Subsequent chapters deal with applications in basic areas of inorganic, coordination, and organic compounds. These include the effects of pressure on spin states and various geometries; pressure effects on organic molecules; applications in geochemistry, conductors, forensic science, and lubricants; and miscellaneous topics such as metallic hydrogen, metallic xenon, and CuCl.