After radiography, white-beam X-ray topography (XRT) is the simplest X-ray imaging technique for crystals. An X-ray topograph is formed by a Bragg reflexion and is in effect a high-spatial-resolution Laue ‘spot’. Synchrotron radiation has given XRT additional powers, with its broad continuous spectrum, small beam divergence, high intensity, strong polarization and regular pulsed time structure. Each Laue image, however, may consist of the superposition of several harmonic reflexions. Background scattering should be attenuated to improve signal-to-noise ratio; and Laue spots should not overlap. This may impose a minimum distance between specimen and detector, possibly at the expense of spatial resolution. Account may need to be taken of absorption of the X-rays, both in the crystal and in air. The configuration of the experiment must be chosen carefully to minimize geometrical image distortions. The detector may be an image plate or a charge-coupled device; but for the best resolution (1 or 2 µm), a photographic plate is used to image individual dislocations. Whole specimens may be illuminated with synchrotron X-rays, or regions may be selected by slits. In the former case, crystals may be checked for distortions or for twinning. In the latter, an image may be made of a slice precisely parallel to a chosen crystallographic plane, as the crystal selects the appropriate ‘Bragg wavelength’ from the continuous spectrum: (a technique only available to characteristic radiation in special cases). Crystalline defects and strains associated with crystal growth, plastic deformation, phase transitions, polytypes and magnetic domains may be studied non-destructively by XRT.