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The characterization of finely divided and structurally imperfect solids is required in the study of many classes of materials, e.g. ceramics, catalysts, decomposition products. Diffraction line broadening is influenced by the microstructure of the solid and is a valuable technique for a unique characterization of a material in terms of size and morphology of crystallites (a region over which diffraction is coherent) and imperfections (microstrains, d- spacing fluctuations, stacking faults, etc). The extraction of these features has traditionally been based on the study of individual diffraction lines, which restricts the analysis to a limited number of directions of diffraction vectors. The complexity of most powder patterns has been a serious impediment to the widespread use of the procedure for detailed microstructural characterization. The advent of fitting techniques, with the use of structural information (Rietveld method) and without structure model (pattern decomposition method) have extended the frontiers of diffraction line profile analyses. In the Rietveld method it has been recommended to have a prior knowledge of the origin and lattice direction dependences of the imperfection effect before embarking in the modelling of line broadening through the pattern. This modelling can be carried out with pattern decomposition methods, which provide individual diffraction lines for a subsequent study of microstructural properties. Several aspects of this technique, performances, limitations and practical problems are reviewed and discussed. Applications to oxides with high specific surface-area are used to illustrate the detailed microstructural information contained in a powder diffraction pattern.