Concepts of an emission mean temperature and a transmission mean temperature are introduced and shown to be effective and necessary in characterizing the radiative emission and transmission of an inhomogeneous non-isothermal non-gray medium. Based on a two zone model for a CO2/H2O/N-2 mixture, the mathematical behavior of these two mean temperatures and their dependence on the temperature and the partial pressure of the absorbing gases of the two zones are illustrated. Results show that the average temperature is not appropriate to be used in the prediction of radiative emission and transmission in practical engineering systems. (C) 2013 Elsevier Ltd. All rights reserved.