International organizations use a bewildering variety of voting rules. Courts, commissions, councils, and the General Assembly use majority rule. The WTO, the International Seabed Authority, the IMF, the World Bank, and the Security Council use various types of supermajority rule, sometimes with weighted voting, sometimes with voters divided into chambers that vote separately, sometimes with vetoes. The voting rules in the EU defy any simple description. Al Sykes and I try to bring some order to this mess in our new paper.