When Frank Hawthorne (1988) edited the Reviews in Mineralogy volume on "Spectroscopic Methods in Mineralogy and Geology," all the experiments presented had been performed at room pressure and room temperature because, at that time, vibrational and X-ray techniques were already quite difficult at ambient conditions so more sophisticated sample environments were not a priority. However, it has now become somewhat easier to perform experiments in situ at high temperatures (HT), high pressures (HP) or under combined high temperature and pressure (HP-HT). These types of experiments are becoming routine on crystals, glasses and liquids (see Shen and Wang 2014, this volume). High-temperature experiments are important because most of the physical properties of high-temperature liquids, such as magmas and melts, are related to their atomic structure. Consequently, it is important to probe the local environment of the atoms in the sample under the conditions noted above (e.g., HT). However, at very high temperatures 1200 C) it is difficult to use conventional furnaces because of a number of experimental difficulties associated with their use: temperature regulation, thermal inertia and spatial obstruction of the sample Due to the progress made in the development of lasers and X-ray, neutron and magnetic sources it is now possible to perform experiments in situ at HT, HP and HT-HP on samples of millimeter or micron size.