Over the last two decades, large-scale project endeavors or major programs that typically deliver a substantial physical infrastructure or a complex product with a lifetime that can extend for decades and across industries have become the norm for many utility sectors, such as transport, energy, water, or food. The allure of ever-larger projects shows no sign of fading away in the face of sustainable development and grand societal challenges – quite the contrary. A significant policy perspective and the trend points to the new generation of large-scale projects, which in contrast to the early industrial era in the US and Europe, compels efforts that require management to minimize affecting the surrounding societal environment. Besides, today's modern infrastructure projects tend to involve a more complex network of organizations – “global” organizations – yielding a dynamic component in project organizing. Large-scale projects are complex endeavors embedded in highly institutionalized social structures and technologies, including public and private actors with various rationalities, modes of collaboration, and project management competencies. These projects evolve, arising as inherently societal concerns, and then shift to technical problems and vice-versa, introducing inertia, organizational path-dependency, and lock-ins. Thus, large-scale projects pose enormous temporary organizing challenges under conditions of institutional complexity, creating “wicked problems” for their management. Hence, the questions of how these large-scale projects as inter- organizational collaboration unfold, and how they can be organized despite these challenges have become crucial in academia and practice alike. Scholars from different disciplines have picked up these questions of organizational, and technological issues in large-scale infrastructure project organizing and have put forth valuable insights into such endeavors. Through the exploratory and elaborated case-based research, this thesis contributes to the debate on large-scale project organizing by advancing an institutional perspective. In line with the overall research aim and conceptual framing, the research design has a qualitative nature and relies on a process approach. The thesis draws from in-depth case studies of project-based processes in the division of Adif - the Spanish Administrator of Rail Infrastructure and ProRail (Adif’s counterpart, the manager responsible for rail infrastructure in the Netherlands), among other principal contractors and suppliers involved in the project(s). The thesis provides a rich empirical examination; it shows that to understand large-scale project organizing, there is a need to change the ontological priorities that underpin the mainstream literature on behavioral studies in project management. The thesis develops nascent theorizing on how the in-between temporary and permanent (inter-) organizational nature of large-scale projects in the presence of institutions narrates the emergence of processes, e.g., path-dependence, and lock-in. A conceptualization of path- shaping and project actors’ agency that bridges the gap between the intra- organizational and institutional level efforts is promoted. The managerial implications of this thesis are two-fold. First, the appended papers put forth among other frameworks and process models that are indeed useful to be utilized. They outline ideas relevant because they lay the groundwork for project managers to extend their efforts beyond the micro- managing of tasks. In particular, Paper A develops the lock-in process model that can be useful for project managers. Secondly, the thesis gives countless advice and managerial implications. The most important being the consideration of heterogeneity in large-scale project contexts in the multi- organizational setting and their interdependencies in broad project networks. They represent the sources of variation in the desired outcomes. Accordingly, Paper B suggests attention needs to be directed to the understanding of the industry – as the field-level institution and its (inter-) organizational components in the context as an essential feature of project management practice. In other words, this thesis suggests that embeddedness in large-scale infrastructure projects is of crucial importance. To this end, Paper C and D propose means for a responsive and active project owner organization, that are essential for effectively interacting with other actors, and for selecting and managing both contractual and trust-based mechanisms effectively.Conclusively, the thesis suggests that project managers’ institutional knowledge in large-scale project settings is equally important, if not more, than the economic or engineering expertise.