The present invention provides a high flux X-ray source 100 comprising a sealed X-ray tube contained within an X-ray shield (101), an optic housing 103 containing a multi-layer optic for collecting and focussing X-rays generated in the sealed X-ray tube, and an X-ray beam conditioner 104. The multi-layer optic 103 is located at a predetermined distance from the sealed X-ray tube 101, with the optic housing 103 being adjustable relative to the sealed X-ray tube 101 and the beam conditioner 104 adjustable relative to the optic housing 103. The use of a multi-layer optic provides for the efficient collection and focussing of X-rays generated in a compact sealed tube and wavelength selectively enables it to act as a monochromator, providing a beam of X-rays with a predetermined range of photon energy.