Constructed wetlands are engineered treatments designed and constructed to utilize physical, chemical, biological, and natural processes involving wetland vegetation, soils, and their associated microbial communities to assist in treating wastewater. Nitrogen removal in constructed wetlands is heavily influenced by environmental factors such as pH, temperature, oxygen, operational strategies, presence of organic carbon, hydraulic load, retention time, pollutant load, and recirculation. This thesis aims to review and investigate the use of constructed wetlands for nitrogen removal from agricultural runoff. A field study at the Halmstad University experimental wetland facility was conducted to determine the nitrogen removal capacity in different seasons and at different temperatures, water residence times, and depths. In addition, an analysis of the impact of dissolved organic carbon (DOC) concentration on nitrogen removal was conducted using a microcosm laboratory experiment. Results from the treatment wetlands showed no significant removal difference between summer and winter. The investigation of hydraulic retention time showed that maximum removal was achieved within 4 days. There was no significant difference in removal efficiency between shallow treatments and deep treatments. Based on the microcosm experiment, there was no significant nitrogen removal difference between treatments with no addition of DOC, 5mg/l, and 10mg/l addition of DOC. However, there was a significant decrease in removal efficiency for the treatment with the addition of 20 mg/l.