Experimental methods proposed for the measurement of the absorption coefficient of light in air are analyzed. The calculations are primarily intended for the wavelength region where, for certain wavelengths, the absorption coefficient to be measured is estimated to be of the order of . 000000001 per cm. The effects of scattering, heat conduction, static and acoustic pressure variations are examined and are related to the problem of detecting the signals produced by the absorption of heat from the laser beam. Both pulsed and cw schemes are considered. The measurement of the static pressure rise in a narrow tube appears as a feasible, although marginal method which offers some hope of success. Also, an interferometric method appears feasible. Finally, the absorption coefficient of the 10.6 micron carbon dioxide laser beam was measured in air.