Power inequalities and mistrust have characterized many relationships between states over the centuries. One approach that states can take to deal with these two, often interrelated, problems is to create intergovernmental institutions and arrangements designed to accommodate the interests of states with varied power capabilities. The Commonwealth of Independent States (CIS) embodies an interesting institutional design in an effort by former Soviet Union (FSU) countries to address these dilemmas. The CIS was not only the first multilateral FSU organization created following the collapse of the Soviet Union, but it also provided a necessary and important framework for the further construction of bilateral and multilateral relations among the former Soviet republics as they reengaged one another. CIS arrangements have been augmented by extensive bilateral negotiations and treaties and, brought together, these interconnected multilateral and bilateral instruments yield a system of cautious regional security governance and framework for international relations within the FSU. This paper analyzes three key features of this foundational CIS institutional design: (1) legalism, (2) an à la carte choice of treaty instruments, and (3) nested bilateralism, wherein many details of the regional, multilateral agreements are implemented via bilateral treaties (hence constituting a combination design feature). Empirically, the paper illuminates this institutional design using a unique dataset of all multilateral security treaties of the CIS (approximately 185) and all bilateral security treaties (more than 500) between the regional hegemon, Russia, and the smaller CIS members. We further investigate the causal mechanisms of the CIS institutional design as it copes with the conditions of hegemony and