Economic theorists of international environmental cooperation and regime theorists who focus on the environment ask the same two basic research questions: why does international environmental cooperation emerge in some cases, but not in others, and why is cooperation wide and deep in some cases, but not in others? Unfortunately, the two schools of thought do not collaborate much in their respective attempts to answer these and related questions. Instead, mutual neglect is the general rule. This paper explores how regime theory can learn from the findings of the economic theory of international environmental cooperation and vice versa, and it examines the prospects for reciprocal learning. An exploitation of mutual learning opportunities is likely to lead to a more comprehensive understanding of international environmental cooperation, and it can ultimately result in better policy advice.