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A critical review of adsorption methods that are currently used in the characterization of ordered organic−inorganic nanocomposite materials is presented, and the adsorption methodology that is potentially useful for this characterization, but has not yet been applied, is discussed. The ordered organic−inorganic nanocomposites include surface-functionalized ordered mesoporous materials (OMMs) with siliceous frameworks (synthesized either via postsynthesis surface modification or via direct co-condensation method), periodic mesoporous organosilicas, and surfactant-containing OMMs. This review covers the methods for determination of the specific surface area and pore volume. The available methods for mesopore size analysis are critically compared and evaluated, with special emphasis on the recent developments related to the application of advanced computational methods for studying adsorption in porous media and to the direct modeling of adsorption using highly ordered surface-functionalized OMMs as model adsorbents. The review also covers adsorption methods for studying the surface properties of organic−inorganic nanocomposites, including those based on adsorption of molecules of different polarities. An emphasis is placed on the emerging opportunity for studying the surface properties of nanocomposites using low-pressure adsorption of nonpolar molecules, such as nitrogen and argon. The opportunities and challenges in adsorption characterization of specific surface sites, uniformity of coated or bonded layers, bonding density of groups on the surface, type of surface species, and so forth, are presented. Thus, this review provides an overview of adsorption studies dealing with organic−inorganic nanocomposites, a critical discussion of adsorption methods available for such studies, and some recommendations for thorough characterization of these materials using gas adsorption.