Abstract: A method is presented which uses glancing-angle X-ray fluorescence techniques to determine the roughness of a target surface. A primary X-ray beam is incident upon the target surface at an angle of incidence of less than about 0.2 degrees. Intensities of the elastically scattered primary radiation peak and at least one emitted secondary radiation peak are recorded. The experimental conditions are varied, preferably by changing the angle of incidence of the primary beam slightly, to generate a set of scattered primary and emitted secondary peak intensities. The secondary peak intensity may then be plotted against the scattered primary peak intensity. The plotted points form a line, and the slope of the line is determined. This slope depends on the roughness of the sample surface. The exact roughness may be obtained by comparing the slope to calibration data obtained using direct roughness measurements by a technique such as atomic force microscopy.