Pressure, together with temperature, composition, or external fields, alone or in combination, can be used as principal variables in directing and controlling matter as well as for the synthesis of revolutionary new materials. The impact of extreme conditions to science, however, has been previously limited by the available vessels and probes. The last decade has witnessed a significant surge in extreme conditions science, thanks to the development of in situ synchrotron radiation (SR) probes and high-pressure (HP) instrumentation. Extreme conditions directly alter chemical, structural, mechanical, electronic, magnetic, and phonon properties of materials, revealing intriguing behaviors across boundaries between insulators and metals, ferromagnets and superconductors, ordered and disordered, and vigorously reactive and inert compounds. In Earth and planetary sciences, research from simulating experiments at high pressure and high temperature provides key information in understanding processes, dynamics, and formation of the deep interiors. For materials applications such as the search for new energy materials and superhard materials, extreme conditions remain a vast, unexplored field. [ABSTRACT FROM AUTHOR]