The department X-ray diffraction (WPD) comprises methods and instruments used for the analysis of residual stresses, textures, phases and nano-structures. The main task of the department is the user service at our beamlines at PETRA III at DESY. In some cases, sophisticated sample environments for in-situ experiments are developed together with our internal and external users. They are used, e.g., for studying welding processes like friction stir welding (FSW) or laser beam welding (LBW). Another task is in-house research, which is largely carried out in cooperation with colleagues from the Institute of Materials Research. All activities are included in the Research Programme MML of the Helmholtz Association.