A crystal monochromator is a device in neutron and X-ray optics to select a defined wavelength of the radiation for further purpose on a dedicated instrument or beamline. It operates through the diffraction process according to Bragg's law.

Neutron monochromator for the ECHIDNA powder diffractometer at OPAL in Australia. It is made by slabs of [113] oriented Germanium crystals which are inclined towards each other in order to focus down the Bragg reflected beam.

Similar devices are called crystal analyzer for the examination of scattered radiation.