The present invention provides an x-ray beam conditioning system with a Kirkpatrick-Baez diffractive optic including two optical elements, of which one of the optical elements is a crystal. The elements are arranged in a side-by-side configuration. The crystal can be a perfect crystal. One or both diffractive elements can be mosaic crystals. One element can be a multilayer optic. For example, the multilayer optic can be an elliptical mirror or a parabolic mirror with graded d-spacing. The graded d-spacing can be either lateral grading or depth grading, or both.