Book excerpt: A first principles scientific model for predicting the spectral radiance from the auroral thermosphere seen by an earthlimb observer is described. This model, and the resulting Auroral Atmospheric Radiance Code (AARC), describe the energy deposition in the thermosphere by primary auroral electrons and the ensuing effects. The latter include electron production and production of nonequilibrium concentrations of vibrationally and electronically excited states, by photochemical means, and by energy transfer. Relaxation of the states by collisions and radiation is described, and the transmission of the infrared radiation emitted from these states is treated. Currently, the model considers four radiators: the nitric oxide vibrational fundamental and first overtone at 2.8 and 5.3 micro the NO+ fundamental at 4.3 mirco, and the CO2 asymmetric- stretch (NU -3 mode) emission at 4.3 micro. The prompt optically optically thin emitters (NO and NO+) are treated in terms of stored, precalculated tables of efficiencies (photons per ion-pair).