Air pollution models help people to understand the way air pollutants behave in the environment. In principle, a perfect model would enable the spatial and temporal variations in pollutant concentration to be predicted to sufficient accuracy for all practical purposes, reducing the need for measurements. This chapter focuses on Gaussian plume models first, because of their wide application in air pollution dispersion modelling. All air pollution modelling and validation needs some understanding of the underlying meteorology. Consideration of wind in air pollution modelling primarily includes wind direction, wind speed and atmospheric turbulence. Wind speed is important for atmospheric dispersion in different distinct ways. First, any emission is diluted by a factor proportional to the wind speed past the source. Second, mechanical turbulence, which increases mixing and dilution, is created by the wind. Third, a buoyant source (hot or cold) is bent over more at higher wind speeds, keeping it closer to its release height.