This commentary takes up conceptual issues raised in the introduction. Discussing the contributions to this volume, we offer three points. First, the concept of fragmentation needs theoretical clarification, which can be provided to some extent by sociological differentiation theory. We suggest a typology of different types of fragmentation. Second, differentiation theory helps to improve understanding of the different causes of fragmentation. Third, a high level of institutional differentiation is an important characteristic of modernity at many levels of politics. It is not fragmentation per se, but rather the (lack of) coordination of fragmented or differentiated institutions, that is a problem for global governance.

This article presents the International Regimes Database (IRD), an analytical tool designed to (i) move regime analysis from its current emphasis on the use of discrete case studies to the use of a relational database encompassing comparable data on a large number of cases and (ii) facilitate quantitative as well as qualitative analyses of hypotheses dealing with international regimes. The article describes the architecture of this database, introduces some preliminary findings relating to compliance, decision rules, and programmatic activities, and discusses methodological issues pertaining to the use of the database on the part of other scholars. It provides a short and easily accessible introduction to the book-length treatment of the IRD contained in: Helmut Breitmeier, Oran R. Young, and Michael Zürn, Analyzing International Environmental Regimes , Cambridge, MA: MIT Press, 2006.