International environmental regimes--especially those regimes articulated in multilateral environmental agreements--have been a subject of intense interest within the scientific community over the last three decades. However, there are substantial differences of opinion regarding the effectiveness of these governance systems or the degree to which they are successful in solving the problems leading to their creation. This article provides a critical review of the literature on this topic. It extracts and summarizes what is known about the effectiveness of environmental regimes in the form of a series of general and specific propositions. It identifies promising topics for consideration in the next phase of research in this field. Additionally, it comments on the research strategies available to pursue this line of analysis. The general conclusions are that international environmental regimes can and do make a difference, although often in conjunction with a number of other factors, and that a strategy of using a number of tools combined can help to improve understanding of the determinants of success.