introduces the fundamentals of atmospheric radiation transport and basic radiative quantities. It introduces gas absorption and emission and discusses the theories of gas (Rayleigh and Raman) and aerosol (Mie) scattering. These concepts are combined in the radiative transport equationRadiative Transport Equation. The chapter also reviews the attenuationAttenuation of radiation by turbulenceTurbulence processes, atmosphericRefraction refractionAtmospheric refraction (El-Mirage effects), and visibilityVisibility.