Three generations of synchrotron radiation sources have revolutionized our understanding of various correlations in the equilibrium phase of materials through X-ray imaging, spectroscopy and scattering techniques. It is anticipated that new sources based on energy-recovery linacs and X-ray free-electron lasers will deliver X-ray pulses that are below a few-hundred femtoseconds in length and have very high coherence. These sources will extend and broaden our current knowledge of materials science. But more importantly, it is expected that these sources will provide the first glimpse of nonequilibrium processes in materials, including nonthermal melting, metal-insulator transitions involving nonequilibrium phases, laser-induced catalytic oxidation, and determining the structure of imperfect nanoparticles lacking crystalline structure. (C) 2002 Elsevier Science B.V. All rights reserved.