Anthropogenic emissions leading to atmospheric aerosols have increased dramatically over the past century. Airborne particles have been implicated in human health effects, visibility reduction in urban and regional areas, acidic deposition, and altering the earth’s radiation balance. The atmosphere subjects aerosol particles to an array of transport and transformation processes that alter their size, number, and composition; the transformation processes include condensation and evaporation. homogeneous nucleation, coagulation, and chemical reactions. A major goal of our research has been to use first principles to gain a predictive understanding of the physical and chemical processes that govern the dynamics, size. and chemical composition of atmospheric aerosols. We review here the current state of our ability to model this atmospheric aerosol behavior.