Meteorology is the key to understanding air pollution patterns. Meteorological data are the driving force for air dispersion models and may also be used to predict the probability of future impacts. The near surface temperature controls the buoyant component of atmospheric turbulence. The variation of temperature with height is used to determine the stability class of the atmosphere. Contaminant concentrations decrease with increasing wind speed as a result of dilution. Wind speeds increase with height due to reduced surface friction. The pattern of wind directions influences directly the ambient levels of contaminants at receptors. The mixing height is the vertical extent through which the pollutants can be mixed. Temperature inversions produce a very low mixing height which increases ambient concentrations. Meteorological services include measurements, basic data, processed data, model input files, standard and enhanced analyses and expert testimony. Meteorological data are important in their own right for building design and safety analyses.