As the degree of difficulty in synthesizing single crystals at high pressure and temperature increases, powder X-ray diffraction becomes a primary technique for determination of crystal structure, unit cell parameters as a function of pressure and temperature, and phase transformations. The use of intense synchrotron radiation has revolutionized high-pressure and high-temperature research. Increases in X-ray intensity by several orders of magnitude have enabled researchers to study very small samples and collect diffraction data in time scale on the order of a minute. Such advances have opened new possibilities for studying materials under extreme high pressure and temperature conditions and time-dependent kinetic problems. Diamond-anvil cell and large-volume multi-anvil apparatus are the primary high-pressure tools used to simulate pressure-temperature conditions of Earth and planetary interiors and to study material properties and phase transformations at high pressure and temperature. The coupling of these techniques with synchrotron X radiation has made in situ diffraction measurements possible at simultaneous high pressure and temperature. Increasingly fast accumulation of in situ data has dramatically increased our knowledge of material behavior at high pressure and temperature. In this paper, we review high-pressure and high-temperature techniques used at synchrotron facilities. Each technique has its own advantages and disadvantages that determine its own unique capability and applications. The large-volume apparatus, capable of generating high temperatures (>2000°C) at moderate pressures ( 100 GPa) at moderate temperatures (<900°C), has been extensively used for in situ measurements of P-V-T equations of state and non-quenchable phase transitions in metals, oxides, and sulfides. We also review synchrotron powder X-ray diffraction techniques and optical arrangements used for data acquisition at high pressure and temperature. Although the energy-dispersive diffraction technique has been the …