Environmental protection programs have successfully improved water quality over the past few decades through the control of point sources of nitrogen. However, control of non-point sources of nitrogen, such as atmospheric deposition, leaking septic systems, runoff and agricultural runoff, has lagged. There is unanimous agreement that arresting nitrogen influxes into aquatic ecosystems is essential to control eutrophication. Protecting drinking water sources from elevated levels of nitrate and nitrite nitrogen from non-point sources is also necessary to protect public health. Elevated levels of nitrate and nitrite in drinking water are known to cause methemoglobinemia (blue-baby syndrome) in infants. The overall objective of this research project was to develop a robust and efficient bioretention system to control non-point sources of nitrogen. Two pilot-scale denitrifying bioretention systems were investigated, one was configured for autotrophic denitrification (S:OS unit) and the other was configured for heterotrophic denitrification (Denyte unit). The experimental program tested the performance of the bioretention units under both laboratory and field conditions. A synthetic stormwater, intended to mimic nitrogen levels in runoff from agricultural croplands, was utilized as the influent during laboratory testing. Water from a waste treatment lagoon located at a dairy farm in Northeastern CT was used as the influent during field testing. Laboratory testing resulted in an average of 63% (S:OS) and 93% (Denyte) TP removal, 92% and 88% TN removal, 80% and 88% NH4 + removal and >95% (S:OS and Denyte) NO3 - removal. Typical field results showed an average of 68% (S:OS) and 62% (Denyte) TP removal, 55% and 42% TN removal, , 88% and 73% TSS removal, 89% and 75% VSS removal, 43% and 35% COD removal, and 65% and 34% BOD5 removal. Breakdown of particulate organic N and ammonification appeared to limit the extent to which TN removal could be achieved during the field testing of the bioretention units. The results of this research project demonstrate that bioretention units can be used to achieve nitrogen removal from stormwater runoff. However, the characteristics of the stormwater runoff will dictate the performance of the bioretention units. Laboratory results showed that bioretention units can achieve excellent TN removal from runoff that is characteristic of agricultural croplands. Field results showed that the treatment of high strength runoff from dairy farm waste treatment lagoons was challenging for the bioretention units. Comparison of results revealed that the Denyte unit performed better than the S:OS unit.