This chapter summarizes selected illustrations of nitrate pollution of groundwater, particularly as a consequence of agricultural usage of fertilizers or land disposal of domestic wastewaters. The purpose of this review is twofold: (1) to demonstrate the widespread problem of groundwater pollution by nitrates, and (2) to identify the influence of various climatological and hydrogeological factors, fertilizer application practices, and subsurface transformation and transport and fate processes on resultant nitrate concentrations in groundwater. It should be noted that Chapter 1 contains a summary of a recent 5-year survey of pesticides and nitrates in drinking water wells in the U.S. The reviewed illustrations in this chapter are divided into those from: (1) the U.S., and (2) Europe and other countries. A summary section concludes this chapter.