Many multilateral environmental agreements (MEAs) have adopted differentiated rules for groups of countries, based on the recognition of their different circumstances, such as special needs of certain parties, or their different contribution to the environmental problem addressed. This results in differences in the stringency or timing of obligations, or in international financial or technological assistance. Differential treatment may be a precondition for some parties to enter the agreement in the first place, but it may make broader cooperation more difficult in the long term. Using a comparative design and process tracing, I consider the factors that led to the inclusion of differential treatment provisions during the bargaining phase of several MEAs. Following the literature on rational design, I expect that the level of heterogeneity across parties, the complexity of the issue under negotiation and the expected costs of reaching the agreement’s goals influence whether and how differential treatment is included.
