This tutorial paper describes how various transport phenomena affect the atmospheric structure. These basic principles are applied to the Earth's atmosphere, but can be extended to any other atmosphere. Two types of movements are considered, namely global movements which affects all constituents and minor constituents movements which depend on the nature of the atmospheric components. Since the atmospheric composition depends on the actual hydrodynamicai regime, the transition from perfect mixing to molecular diffusion is analyzed as well as the transition from collisional dominated heterosphere to the exosphere where almost no interaction occurs between atmospheric components.