In capital-intensive organizations formed to plan new infrastructure development projects, the promoter of the project (as a single organization or as part of a coalition) rarely controls all of the critical resources required to achieve the system-level goal. Instead, the direct control of interdependent resources is diffused across multiple legally independent stakeholders (Lundrigan, Gil and Puranam, 2015). As such, the core structure in these so-called 'megaproject' meta-organizations is a classic empirical instantiation of a pluralistic setting (Denis, Langley and Rouleau, 2007). In pluralistic settings, the authority to make strategic decisions is diffused across actors with heterogeneous objectives, interests, values and expertise. Hence, to achieve the goal, the promoter needs to cooperate with multiple stakeholders. Since some critical resources are not transactional or measurable, the cooperation problem is not a 'buy' problem. Instead, resolving the cooperation problem necessitates a search for mutually consensual solutions that reconcile conflicting interests. Moreover, this search unfolds without recourse to top-down authority characteristic of unitary organizations. Therefore, the promoter has to play a coordinating role that traverses organizational boundaries to coalesce competing preferences into a one-off plan. Against this backdrop, this doctoral research investigates how designed rules and structures influence consensus-building during the collective development process. We conduct the research by drawing on two cognitive lenses consolidated in two vast bodies of literature that have remained largely disparate: organization design (Puranam, Alexy and Reitzig, 2014; Burton & Obel, 1984; Lawrence & Lorsch, 1967; March & Simon, 1958; Mintzberg, 1979) and collective action (Ostrom 1990, 2005). Combining these two research streams allows us to investigate how to resolve the coordination and cooperation problems inherent in pluralistic settings. Our research method is a single case study with embedded units of analysis. This method allows us to probe deeply into operational details while maintaining the holistic features of the focal phenomena (Yin, 2009; Yin, 2013; Siggelkow, 2007; Eisenhardt & Graebner, 2007). Our focal case is the planning stage of High Speed 2 (HS2), a new multi-billion-pound cross-country railway project in the UK. The scheme is promoted by the UK Government. However, the planning effort has required that the Government share local decision rights for planning choices related to the stations along the route with multiple local authorities. These local authorities are independent, resource-rich stakeholders who are impacted by local choices, and they have deep knowledge of local needs and constraints. Thus, in the HS2 case, organizing for collective action is a prerequisite for achieving the system-goal. Our research presents two major theoretical contributions. First, we contribute to organizational design literature by advancing our knowledge of how organizations can be designed to achieve system-level goals when decision-making authority is diffused across multiple organizational boundaries. Specifically, we advance our conceptual understanding of polycentric systems--a form of organizing that distributes decision-making authority across multiple local groups of independent stakeholders. As such, we illuminate the designed processes and structures that enable the core actors in a polycentric system to integrate effort and reconcile their differences over time. Organization design choices are about designing governance structures that enable and constrain collective action. Hence, we also contribute to the project management literature with insights on the governance of the planning stage of megaprojects. Specifically, we offer a deeper understanding of how to organize an inter-organizational setting to make planning decisions and manage interdependencies with the environment. Furthermore, we reveal that ambiguous evaluations of megaproject performance are rooted in collective efforts to resolve coordination and cooperation problems. Our research is grounded in the planning effort for the HS2 project and thus embedded in the UK context. We, therefore, encourage future studies to investigate the generalizability of our claims on organizing for collective action in other institutional contexts.