The paper describes the removal of nitrogen in horizontal sub-surface flow constructed wetlands (HF CWs) for various types of wastewater. The survey includes more than 900 annual means from more than 300 systems in 36 countries that were categorized into municipal, industrial, agricultural, and landfill leachate. The results revealed that the highest average concentration of total nitrogen (TN) was found in landfill leachate (211 mg l⁻¹), while the highest average loading (3,080 g N m⁻² yr⁻¹) was recorded for systems treating wastewater from industrial operations. The average inflow TN concentration and loading for all systems were 63 mg l⁻¹ and 1,158 g N m⁻² yr⁻¹, respectively. For ammonia-N the results were similar — the highest average inflow concentration (162 mg l⁻¹) was recorded for landfill leachate and the highest average loading was recorded for agricultural wastewaters (2,722 g N m⁻² yr⁻¹). The results also indicated that there is a good relationship between inflow and outflow concentrations and loadings for both TN and NH₄-N. Harvesting aboveground biomass of emergent macrophytes in HF CWs removes only limited amount of nitrogen as compared to inflow load (commonly < 10%).