Pesticide molecules in soils undergo different processes of biological, physical and physico-chemical origin, and occurring over different time (minutes to decades) and spatial (nm to km) scales. Pesticides are represented by a diversity of molecules having contrasting physico-chemical properties inducing various kinds of behavior in terms of persistence, sorption, transport with the potential for contamination of water, uptake by plants, and possible impacts on soil biota and microbial processes. This chapter proposes an update of current available knowledge on the main processes and current state of the art of knowledge integration in pesticide fate models at the plot and watershed scales for environmental risk assessment.