Money and multilateralism: how funding rules constitute IO governance

International relations scholarship largely accepts that multilateralism lies at the heart of the liberal international order and is instantiated in formal, intergovernmental organizations. This paper revisits the conventional wisdom regarding the multilateral character of international organization (IO) governance by drawing attention to the funding methods used to finance contemporary IOs. I argue that different funding rules constitute different modes of governance. While mandatory funding rules are easily reconciled with traditional conceptions of multilateralism, voluntary rules are not. In particular, restricted voluntary funding rules devolve authority over funding decisions to individual actors, undercutting the collective decision making that is central to multilateral governance. I demonstrate the relevance of the argument in the case of the United Nations, which has transformed from an institution reliant primarily on mandatory contributions, to one disproportionately reliant on restricted, voluntary funds. The counterintuitive result is an increasingly bilateral United Nations. The paper contributes to our understanding of the relationship between multilateralism and IO governance, and has implications for literature related to institutional design, delegation, and development aid. In addition, it raises empirical and normative questions regarding reliance on voluntary funding.