Characteristics of spatial and temporal fluctuations of atmospheric absorption and emission at millimeter and centimeter wavelengths are presented. Theoretical relations and experimental data are given on structure functions of absorption and brightness temperature at wavelengths of 0.8 and 1.35 cm. It is shown that in cloudless weather the intensity of fluctuations at these wavelengths is determined mainly by random fluctuations of the humidity field. Under cloudy conditions the intensity of fluctuations of microwave atmospheric radiation grows, with stratiform and cumuliform clouds differently affecting the character of the space-time dependency of fluctuations.