An understanding of long-range transport of air pollutants in the atmosphere requires a knowledge of the relevant atmospheric dynamic and chemical processes active at the regional scale as well as the temporal and spatial distribution of emissions. Numerical modeling is the most efficient way to determine the atmospheric transport, phohemistry and deposition pathways. The book therefore discusses the physical and chemical processes that determine regional air pollution and presents the relevant modeling techniques to describe the different atmospheric processes that are active at that scale.