Gas adsorption techniques constitute the most common approach for the characterization of the pore structure of porous materials, and undoubtedly, N-2 adsorption at 77 K is the most used. However, N-2 adsorption has some limitations. Therefore, to achieve the correct assessment of the microporosity, the use of other adsorptives has been proposed. In this sense, it has been demonstrated that CO2 adsorption at 273 K, at sub-atmospheric pressures, is necessary for the correct characterization of this narrow microporosity. In this keynote, the usefulness of the adsorption of gases to characterize different type of microporous solids will be reviewed.Small Angle Scattering (SAS) techniques represent an alternative to gas adsorption methods. A review of the first experiments performed with single activated carbon fibers with the micro-SAXS technique available at the ESRF (synchrotron facilities) will also be reviewed.