This document sets out the characteristics of instruments used for X-ray powder diffraction (""powder"" as defined in EN 13925-1:2003, Clause 5) as a basis for their control and hence quality assurance of the measurements made by this technique. Performance testing indicators are given for diffractometer performance testing. Different types and makes of X-ray powder diffractometer vary considerably in their design and intended fields of application. This document attempts to cover as much of this range as possible by keeping to common principles. To make the standard more readily applicable, the Bragg-Brentano configuration is addressed in most detail becau