When exclusivity becomes a liability: Legitimacy and membership enlargement in the OECD

International organisations (IOs) rarely revise their membership rules. Yet what explains such changes when they happen? We argue that IOs may alter membership rules to prevent or address threats to their legitimacy, such as those arising from shifts in the global distribution of power or the normative environment. Empirically, the article examines the features and determinants of changes in the Organisation for Economic Co-operation and Development (OECD) membership rules. The OECD has expanded and diversified its membership, especially since 2004, admitting more non-European and self-identified developing countries. The article also advances a framework that maps IO membership rules along two dimensions: selectivity by ascription and selectivity by standards, yielding four ideal types of membership arrangements: universal, ascriptive-selective, standards-selective, and closed. Each dimension poses a legitimacy trade-off: ascriptive selectivity can alienate an excluded majority yet relaxing it may dilute the shared identity that makes membership valuable; highly demanding standards signal that membership is meaningful yet may exclude states that would widen the IO’s reach. Applying this framework to the OECD, we show how legitimacy erosion prompted it to shift from ascription-based towards standards-based forms of selectivity. This case indicates that IOs can redraw the boundaries of membership as part of a struggle for legitimacy, without abandoning exclusivity itself.