Dissolved organic nitrogen (DON) is present in raw and finished drinking waters, although the DON concentrations have not been determined. DON analytical techniques have been established by marine scientists and freshwater ecologists, but have not been applied to drinking water systems specifically. Based upon United States Geologic Survey (USGS) water quality monitoring data, over 23,000 water samples for DON were calculated. The 50th percentile DON concentration, that were not below the detection limit of 2 mg-N/L, for surface water (0.34 mgN/L) was greater than the groundwater concentrations (0.24 and 0.17 mgN/L for shallow and deep groundwater, respectively). During drinking water treatment the removal of DON by different chemical and physical treatment processes is unknown. Model organic nitrogen material is reactive with oxidants and can form disinfection byproducts. Most DON in natural waters are considered to be proteinaceous material or recalcitrant high molecular weight humic-like material. This paper presents an overview on DON occurrence, measurement, reactivity, and treatment. Includes 28 references, table, figure.