The purchase of a single crystal X-ray diffractometer for the Department of Chemistry and Biochemistry of the University of Bern is proposed through this R'Equip project. This instrument is absolutely necessary to carry out research at high level in the department, mainly because suitable equipment is currently lacking. A previously installed CCD diffractometer, from the former institute of chemical and mineralogical crystallography, is no longer working. Moreover, the recent progresses in detectors, sources and optical focusing makes it necessary to use a X-ray diffractometer of new generation to maintain the high level of the research and to start new and innovative projects as well. The research groups mostly interested in the new equipment are: a) the recently established chemical crystallography group, b) the groups active in material science and inorganic chemi-stry and c) the groups researching in organic and bio-organic chemistry.The instrumentation will be used for the accurate determination of the electron density distri-butions in molecular crystals, the study of transformations in the solid state (on varying temperature or pressure), the analysis of diffuse scattering to obtain structural information on disordered species, the accurate determination of supramolecular architectures in new materials, the analysis of molecular geometries and stereochemistries. The main requirements for the equipment are: a) the instrument shall enable high resolution data collection working with Mo radiation (very important for studies on accurate electron den-sity distribution, solid state phase transitions and diffuse scattering); b) the detector shall be areal (CCD camera or imaging plate) in order to allow rapid data collections and extensive im-aging of the reciprocal space (not only at Bragg positions) and it shall be sensitive enough for the accurate measurements of even weak X-ray diffracted intensities; c) the goniometer shall enable extensive mapping of the reciprocal space and shall be compatible with the low temperature devices already in use in the chemical crystallography laboratory; d) the radiation source shall be of high intensity and homogeneity to improve the signal detection. Combination of this instrumentation with equipment for low temperature, already available, will make the laboratory at the frontier in chemical crystallography. The diffractometer will not be used for service purposes, but for advanced researches in structural chemistry. We envisage also the use of the instrument for educational purposes, to continue the well established tradition of chemical crystallography at the university of Bern. This might include cooperation with industries to start educational programs for industrial researchers.