Risk assessment and management of pesticides are directly related to the sustainable agriculture concept because, besides playing an important role in intensified agriculture by protecting crops from pests and diseases and reducing competition from weeds, the use of pesticides can cause human health and ecological problems. Several pesticides have been shown to reduce water quality and result in adverse effects to sensitive organisms, aquatic ecosystems, and human health. Pesticides enter water systems through different pathways and, therefore, it is important to understand the environmental behavior and fate of pesticides and assess their potential exposure and associated risks to the environment. Ecological risk assessment—ERA—has been adopted in many countries for regulatory purposes and as a basis for the management of pesticides. Models can be used during different stages of the ERA process and include fate-exposure models, exposure-effect models, and integrated models. In this chapter, definitions of ERA are stated. Pesticide environmental behavior processes and modeling approaches are briefly discussed. Tools for ecological exposure characterization in the regulatory context of agricultural pesticides concerning surface water and groundwater bodies are presented.