The rapid decline of biological diversity as a result of human activities is a major challenge for the international community. National, regional and international legislation has been introduced to halt this trend. This study reviews the eff ectiveness of the five most significant international biodiversity-related conventions: - The Ramsar Convention - The World Heritage Convention - The Convention on the International Trade in Endangered Species - The Migratory Species Convention - The Convention on Biological Diversity A three-step approach is followed in this study. The first step comprises a survey of the concept of eff ectiveness with respect to international environmental agreements, which leads to a workable definition of effectiveness. The second step involves the development of a practical test the Eff ectiveness Test to determine the effectiveness of the five conventions in relation to the problems they intend to address. The final step concerns the actual examination and assessment of each individual convention on the basis of the Eff ectiveness Test. The findings are certainly worrying; these are testing times indeed.