S ince the first synchrotron radiation (SR) x-ray diffraction (XRD) experi-ment in a diamond anvil cell (DAC) in 1977 [1], the combination of highpressure techniques with different SR spectroscopic methods has become one of the most fruitful experimental techniques. The growing presence of high pressure instruments in the third-generation synchrotrons in different countries suggests that these techniques will remain so in the coming years. The present chapter offers a brief introduction to the applications of some x-ray spectroscopic techniques to materials under extreme conditions, focusing on

structure determination. We do not include examples involving the use of large volume presses (Paris-Edinburgh or multianvil). For these devices, that are increasingly used in large facilities, we refer to References [2, 3]. After a brief introduction on the generation of SR and the basic structure of an SR beamline, we will describe the spectroscopic techniques most commonly used in combination with DACs, then focus on two techniques used for structure determination under high pressure: x-ray diffraction (XRD) and x-ray absorption (XAS), illustrated with several examples in which these techniques have yielded significant results.