X-ray line profile analysis (XLPA) proved to be one of the most powerful tools to obtain detailed qualitative and quantitative information about the substructure of crystalline materials in terms of (i) dislocation structure, (ii) crystallite size and size-distribution, (iii) planar defects, especially stacking faults and twinning and (iv) intergranular strains and stresses. Together with transmission and scanning electron microscopy (TEM and SEM) the three methods strengthen each other in perfect synergy and offer a complex characterization procedure of the microstructure in crystalline materials.