Just like electrons, when an X-ray hits the specimen, a number of interactions are possible. For X-ray diffraction, the wavelength of the incoming incident beam and the diffracted beam must have the same wavelength for constructive interference (diffraction) to occur. Therefore, only the elastic interactions, those which conserve energy, contribute to the diffracted signal that we use in XRD. However, there are many other interactions of the X-ray beam with the specimen. Inelastic scattering such as fluorescence and Compton scattering can be picked up by X-ray detectors, and in this way they contribute to the background that is observed in all lab-scale diffraction measurements.

The scattering of X-rays comes from the electron cloud, and scattering occurs in all directions.