This volume covers aspects of numerical modeling of the atmosphere and climate from the microscales of turbulence to the very large scales associated with climate and climatic change. Each of the three major spatio-temporal scales of the atmosphere, namely, the microscale, the mesoscale, and the macroscale is addressed through a hierarchy of models. Results of model simulations are illustrated throughout the text, with many of these examples based on the author's original research work. For each type of model discussed here, the theoretical background, including governing equation sets, simplifying assumptions, and advantages and limits of the models, is provided. The topic of coupled, or nested, modeling systems as a promising approach to air pllution embedded in regional atmospheric flows, as well as to the regional atmospheric response to global climate forcings, is also addressed. An attempt is made throughout the book to highlight the highly interdisciplinary nature of atmospheric modeling, particularly in those sections dealing with climatic change issues.