Abstract: An extended range grazing incidence monochromator is disclosed which utilizes Rowland circle geometry to select a frequency of radiation from a broad spectrum of radiation, with the entrance slit and the gratings of the monochromator being positionable by remote electrical control, such as that provided by a digital computer, while the exit slit of the apparatus remains fixed. The monochromator has an extended range because it includes two different gratings, each of which has an optical characteristic adapted for use in a Rowland circle of a different size, and the apparatus is capable of switching between two gratings without breaking the ultra-high vacuum contained in the interior of the monochromator. The positioning of the entrance slit and the appropriate grating is accomplished both rotationally and linearly through the use of stepping motors which can be precisely remotely controlled for maximum accuracy and control.