This article presents an overview of the principles involved with physical transport processes determining the fate of substances in the environment after their release from natural or anthropic sources. The first section discusses advective transport produced by the presence of a flow field. The second section discusses diffusion, a concept that describes the transport of the substance combining in a modeling framework the stochastic behavior of individual molecules or particles subject to displacement from their instantaneous position. The third section treats dispersion, which is a model of the fate of the substance which accounts for the spatial distribution of its concentration and for the spatial properties of the flow field.