During 1990 and 1991 the U.S. Environmental Protection Agency (EPA) sponsored an effort to identify existing and planned constructed wetlands in the U.S. and to collect readily available information from operating systems. The inventory documented the presence of over 150 constructed wetland systems for wastewater treatment, including both free water surface (FWS) and subsurface flow (SF) systems. The majority of the systems identified were SF systems for treating municipal wastewater. FWS systems were separated into three groups based on the design level of effluent water quality. SF systems were separated into three groups based on the basic design approach. The inventory indicated that neither between or within these groups was there consensus regarding basic hydraulic and engineering design criteria, system configuration, or any other aspect, such as, type of vegetation, size and type of media, or pretreatment. Information on location, type of systems, design approach, hydraulic and organic loading rates; costs, and other aspects is presented.