Constructed wetlands (CW) are natural wastewater treatment systems which rely on ecosystem processes, such as nitrification and mineralization, for contaminant removal. A typical CW consists of a channel or bed, filled with coarse soil/gravel type material, and planted with aquatic or semi-aquatic plants such as reeds. Wastewater is delivered to the inlet after coarse screening, and is treated by a combination of physical, biological and chemical processes. The efficiency of CW is strongly location dependent, as local weather, among other parameters, can influence biochemical processes. This research program aims at developing the CW technology in the Lebanese environment by optimizing the operating parameters of the soil-water-plant system. The program was initiated in 1992 on pilot scale systems, and has evolved since 1999 to a field-scale operation following the implementation of a life-size system in a convent in Garzouz-Jbeil.