This report documents efforts to quantify and monitor the performance of green roofs. This project investigated green roofs as an approach to control stormwater discharge and pollutant content. The work was carried out by the Penn State Green Roof Center of The Pennsylvania State University at University Park, PA. Prior to this project, EPA had limited information available on the beneficial use of green roofs as a stormwater control due to the limited application of this technology in the United States. The Urban Watershed Management Branch of Edison, New Jersey, as part of the EPA National Risk Management Research Laboratory seeks to develop new urban technologies and assist municipalities in selection of appropriate technologies to control urban wet-weather discharges. This report provides the data and background municipalities and private entities need to move forward with decisions to implement green roofs as a stormwater control technology, or best management practice (BMP). The purpose of this study was to quantify runoff reductions resulting from the use of extensive green roof systems. This project investigated design specifications and materials of green roofs used as stormwater control devices. This was done through replicate experimental setups using small-scale buildings exposed to the elements and in controlled environment greenhouse test bed systems. The size of the buildings allowed the complete volume of runoff to be captured analyzed. Performance data derived from side-by-side field and laboratory tests provide clear performance criteria for stormwater volume control by green roofs. Key water quality parameters evaluated included: real-time, flow, turbidity, electrical conductivity (EC), pH and nitrate; and, grab sample pollution assessment, for nutrients, metals and hardness.