This dissertation introduces an original theory explaining how international organizations (IOs) evolve in response to changing member dynamics. I argue that member states create new subsidiary IOs, which I call linked international organizations (LIOs), in order to “recontract” their cooperation. Three features of LIOs incentivize their creation: 1) they are easy to create, 2) they have flexible design features, and 3) they insulate the original IO from destabilizing reform. I evaluate my theory using a multi-method approach. First, I analyze original data on nearly 1,200 LIOs created since World War II. Statistical tests show that changes in the membership environment at existing IOs – including the addition of new members, changes in the distribution of power, and shifts in member preferences – leads to LIO creation. Second, I examine LIO creation at the United Nations (UN) using historical analysis, quantitative text analysis, and case studies of the Decolonization Committee, the United Nations Conference on Trade and Development (UNCTAD), the United Nations Environment Programme (UNEP), and the Peacebuilding Commission (PBC). Finally, I investigate the creation of LIOs at the World Bank, including case studies of the International Development Association (IDA) and the Global Environment Facility (GEF). My dissertation proposes a major rethinking of reform and evolution at IOs. The creation of LIOs provides states a means to resolve internal disagreements and updates IOs so that they are more reflective of their diverse memberships. This helps maintain (and even expand) cooperation in an increasingly multipolar world.