X rays - discovered by W.C. Rontgen in 1895 - have become established as an invaluable probe of the structure of matter. Progress in understanding the interaction between x rays and matter and of exploiting X rays experimentally has been increasing steadily since its discovery. In more recent times this has lead to unraveling the structure and morphology of compounds of increasing complexity like self-assembling molecular systems, including functional units of bio-organisms like DNA and proteins. MRSEC has funded within the Department of Polymer Science and Engineering an X-Ray Facility with several modern instruments for x-ray scattering (small, intermediate and wide angles), powder x-ray diffraction, and x-ray reflectivity studies of thin films.