These recommendations aim to be a tool for the selection and appraisal of the methods of characterization of porous solids, and to also give the warnings and guidelines on which the experts generally agree. For this purpose, they successively consider the description of a porous solid (definitions, terminology), the principal methods available (stereology, radiation scattering, pycnometry, adsorption, intrusion, suction, maximum buble pressure, fluid flow, immersion or adsorption calorimetry, thermoporometry, size exclusion chromatography, Xenon NMR and ultrasonic methods) and finally the general principles which are worth being followed in the selection of the appropriate method. © 1994 IUPAC