Some techniques are considered to be of prime importance in the study of adsorption phenomena and of heterogeneous catalysis, and they are employed in all research laboratories active in these fields. Volumetry, gravimetry, and reactors of different types, associated or not with gas chromatographs, belong to this category. When a laboratory is regularly involved in studies of gas-surface interactions, the techniques of IR spectroscopy, mass spectrometry, x-ray diffraction, and electrical and magnetic measurements will also be developed. If the laboratory receives good financial support, it will probably invest in EPR, electron microscopes, or in some of the more recent techniques, such as ESCA, LEED, and Auger spectroscopy.