A review of the features of test performances for the purpose of certification of difractometric measuring systems using short-wave radiation (x-ray and neutron radiation) which are intended for diagnostics of phase composition of substances and materials is presented. The main contribution to the uncertainty of the results of phase analyses is made by methodological errors, much more significant than instrumental characteristics of difractometers. The problems of conformity assessment to the claimed characteristics of the corresponding difractometric systems intended for various types of phase analysis are considered. For the identification (referenced as «qualitative» or «semi-qualitative») analysis, various structural databases and sometimes the values of the integral intensity ratios of Bragg reflections of certified standard reference materials (CSRMs) are used. To achieve high accuracy and reliability of quantitative phase analysis calculations of the angular positions of reflections should be performed on the basis on standardized (certified) reference (evaluated) data of crystallographic databases. To assess the reliability of the results, the equipment (difractometric measuring systems) should be tested together with the software and CSRMs sets should be also used. The sets of CSRMs include certified characteristics, i.e. the lattice constants (unit cell dimension), the intensity ratio of Bragg reflections, and/or the mass fraction of the composition of each phase, determined by Rietveld methods, which provide rapid achievement of higher accuracy and reliability. The sets of CSRMs used for testing and especially during operation of difractometers enable specialists and metrologists to ensure high quality and legitimacy of measurement results, which allows further refining of materials engineering technology and ensure the reliability and safety of products.