This chapter focuses on solar radiation and its interaction with the terrestrial atmosphere in the context of the Earth's radiation budget and radiative forcing of climate, as well as its direct impact on atmospheric composition and temperature. The composition, temperature, and motion of Earth's atmosphere are determined by internal chemical and physical processes as well as by complex interactions with other parts of the climate system—notably the oceans, cryosphere and biosphere. On a global and annual average the solar energy absorbed by the Earth is balanced by thermal infrared radiation emitted to space. However, solar radiation absorption has a strong latitudinal variation, while the outgoing infrared radiation has only a weak latitudinal dependence. Thus there is a net surplus of radiative energy at low latitudes and a deficit at high latitudes.