Wastewater-derived dissolved organic nitrogen (DON) accounts for up to 80% of dissolved nitrogen in nitrified-denitrified effluent. The sturdiness of DON measurements hindered the characterization of DON, especially in wastewater matrix, leading to an unsatisfying knowledge level. Measurement of DON and DON species is imortant not only as a measure of treatibility of wastewater in treatment plants, but also for the possible algal growth-stimulating effects after their discharge into receiving waters. In addition, wastewater-derived DON compounds may act as precursors to several disinfection by-products during intentional or unintentional reuse of wastewater. A review of DON compounds in wastewater and wastewater effluents is given.