This paper estimates the effect on international trade of three multilateral organizations intended to increase trade: (1) the World Trade Organization (WTO) and its predecessor the General Agreement on Tariffs and Trade (GATT); (2) the International Monetary Fund (IMF); and (3) the Organisation for Economic Co-operation and Development (OECD) and its predecessor the Organisation for European Economic Co-operation (OEEC). I use a standard 'gravity' model of bilateral merchandise trade and a large panel dataset covering over 50 years and 175 countries. My results indicate that OECD membership has had a consistently large positive effect on trade, while accession to the GATT/WTO also increases trade.