This dissertation analyzes the design of transnational institutions in which states, firms, and NGOs cooperate to govern adverse consequences of global corporate conduct in the areas of conflict prevention and security. Although transnational institutions are typically concerned with prisoners' dilemma-like problems, they often lack the institutional structures required to effectively deal with them. Functionalist, constructivist, and simple rational choice-based theories of international cooperation are weak in explaining such inefficient institutions. I propose a political model of transnational institutional design that places distributional conflict and power at the center of the analysis and links them to formal monitoring and enforcement structures of transnational institutions. Extant work typically focuses on particular forms of power in isolation. A single form of power is, however, rarely a universal source of influence in tripartite institutional bargaining. I argue theoretically and show empirically that states, firms, and NGOs use multiple power variants, such as economic, institutional, and network power to secure favorable institutional choices and that the extent to which different power tools are an effective and efficient means of influence is conditioned by the formality and transparency of the institutional context in which bargaining over institutional structures occurs. As a consequence, changes in the bargaining environment impact the distribution of power among states, firms, and NGOs and, in combination with their preferences, shape institutional choices. Integrating case studies, network analysis, and statistical methods, I draw on data from five negotiation episodes of tripartite institutional bargaining in three transnational institutions—the Kimberley Process, the International Code of Conduct for Private Security Service Providers, and the Voluntary Principles on Security and Human Rights—to probe the explanatory power of my model. This dissertation also makes a methodological contribution that improves researchers' ability to measure the structural properties of large transnational networks constituted by different types of actors.