Chemical fate models require explicit algorithms for computing the effects of transformation and transport processes on the spatial and temporal distribution of chemical concentrations. Transport processes in aquatic systems are driven by physical characteristics on the system and include hydrodynamic transport, sorption-desorption, sediment transport, exchanges between bed sediments and the overlying water column, and volatilization-absorption across the atmosphere-water interface. Chemical transformations include direct and indirect photolysis, hydrolytic reactions and reductions. Biological processes include microbial and algal transformations and biological transport vectors. This paper gives a brief evaluation of the current status of knowledge in each of these areas, indications of the chemical and environmental parameters needed for quantitative descriptions of the process kinetics, and suggestions for further research.