[en] The following are discussed: reasons for using powder method; two main approaches for dealing with overlapping reflections; (1) careful calibration of a diffractometer with known standards whose peak shape functions are then used to strip an unknown pattern producing a set of structure factors which can be used in the usual manner to refine the structure; (2) method developed by Rietveld, which is a least squares procedure whereby the total diffraction pattern is fitted to a model containing parameters which describe the peak positions (cell constants and instrumental aberrations) parameters which describe the diffraction peak shape and its variation with Bragg angle; X-ray sources; techniques for recording diffraction data. Examples are discussed. (U.K.)