Since 1999, the Trilateral Wadden Sea Cooperation (TWSC) between Denmark, Germany and the Netherlands has periodically produced Wadden Sea Quality Status Reports (QSR) describing and evaluating the current ecological status of the Wadden Sea. The QSRs identify changes in this status and their possible causes, classify issues of concern and indicate possible measures of amelioration, including evaluation of the likely effectiveness of these measures. They also indicate gaps in our knowledge. The QSRs are based upon the Trilateral Monitoring and Assessment Programme (TMAP). The programme and the reports were key elements in achieving the inscription of major parts of the cooperation area on the list of UNESCO World Heritage Sites.