AbstractIn recent years, a number of experimental X-ray diffraction techniques have been developed by which a topographical display of the microscopical defects in a crystal can be obtained. This brief review of the most useful of these techniques is intended to summarize the elements of the various methods and to compare their respective features and limitations. Contrary to microradiographic methods, in which image contrast is due entirely to variations in X-ray absorption from point to point in the specimen, X-ray diffraction topography is concerned with point-topoint variations in the directions or the intensities of X-rays that have been diffracted by crystals. From these variations the defect structure of the crystal may be examined. Methods that mainly measure local variations in the direction of the diffracted beam are useful for the detection of gross misorientations such as subgrains or grains (methods of Gui nier and Tennevin, Schulz, Weissmann). Intensity mapping methods are chiefly concerned with individual defects such as dislocations, stacking faults, etc. In both groups there are experimental arrangements with both Laue-case (transmission) and Bragg-case (back reflection) geometry.