During the last three decades, it has become increasingly clear that atmospheric modelling and remote sounding of the atmosphere from space, to name just two important application areas, are affected by non-equilibrium processes which have not been incorporated into traditional radiative transfer calculations. These processes, dubbed "non-LTE", are therefore the subject of growing interest among scholars and researchers dealing with the upper atmosphere. This important book provides the first comprehensive and "global" description of non-LTE infrared emissions in the atmosphere of the Earth a