Herbicides are widely used to control weeds; however, they can have other effects on the environment. Herbicides can move from the site of application through spray drift, volatilization from surfaces, surface run-off or leaching to groundwater. This chapter examines the sources and fate of herbicides in the environment and the environmental effects of herbicides. It also addresses the ways in which the environmental effects of herbicides may be managed and reduced, including the use of herbicide substitutes and mitigation of herbicide effects, and looks ahead to future trends in this area of research.