The role of heating due to absorption of solar radiation by molecular oxygen (O2) in the A, B, and &ggr; atmospheric bands and in the infrared atmospheric band is reviewed. Prior studies have demonstrated the importance of heating by these O2 bands in the vicinity of the tropopause. In the middle mesosphere, the heating associated with O2 atmospheric bands is shown to rival that of the numerous individual solar and chemical heat sources. We show that heating in the O2 atmospheric bands increases the total diabatic (i.e., solar plus exothermic chemical reaction) heating by 5 to 15 percent between 60 and 80 km.