Earth’s atmosphere is tied closely with the Sun. The Sun emits electromagnetic radiation at a wide range of wavelengths. Radiation is transported through the atmosphere by transmission, absorption, and scattering. ‘Atmospheric physics’ outlines the Earth’s radiation budget—the incoming and outgoing radiation, equilibrium between them, and departures from this equilibrium due to increasing levels of clouds, greenhouse gases, and atmospheric aerosols. It then describes the greenhouse gases that absorb and emit radiation and the thermodynamics of the atmosphere. The importance of water, the dominant atmospheric constituent responsible for the loss of radiative energy to space and hence atmospheric cooling, and the electrical energy stored in the atmosphere are also discussed.