Abstract: An X-ray diffractometer has an X-ray source for producing an X-ray beam; a position sensitive detector for detecting diffracted X-rays over a wide angle; and means for effecting controlled relative rotation between the detector and the X-ray source incident beam. A sample holder is capable of rotation about three mutually perpendicular axes and is also capable of providing rotation of the sample relative to the sample holder about two perpendicular axes. Thin films or substrates under investigation can be individually aligned into selected diffraction geometries by such a diffractometer. The X-ray source itself may be rotatable about the axis of the X-ray beam.