As the scale and scope of infrastructure projects have increased, so too has the array of stakeholders either involved or impacted. Such projects often take years to come together and evolve with time through the actions of project sponsors and the engagement of various stakeholders. Stakeholders through engagement and input can help legitimize and improve large-scale project initiatives. Stakeholders can also marshal opposition that can delay or block these projects. Consequently, the significance of stakeholder involvement is critical in megaprojects. Governments have increasingly utilized public-private partnerships (PPPs) for megaproject delivery. This method introduces characteristics that distinguish PPP megaprojects from others such as: private control, profiteering, foreign profits, and long-term concessions. This study investigates whether differences exist between PPP and non-PPP megaprojects with respect to stakeholder involvement strategies and stakeholder issues raised in such projects. This research employed a longitudinal multiple case study approach that examined four tolled fixed crossing megaprojects; two of them were delivered as PPPs and two were delivered as design-build (i.e. non-PPP). The approach followed the design of prior studies in this area by De Schepper, Dooms, and Haezendonck (2014) and Winn (2001). Pre and post milestone event analysis captured trends and shifts in involvement strategies and stakeholder issues. Subsequently, stakeholder issue tables (organized by issue themes) and stakeholder mechanism tables (organized by mechanism type and information flow) were utilized for across case synthesis and comparison to identify similarities and differences. Analysis of stakeholder involvements across cases showed that NEPA establishes a baseline for involvement, but its requirements are not sufficient for megaprojects; a more comprehensive strategy is necessary. Further, although participatory involvements may be beneficial particularly in complex settings, these mechanisms must be carefully managed in terms of process and criteria for evaluating stakeholder input. Additionally, when private partners/contractors are involved in megaprojects, they become part of the project team and support a coordinated involvement approach. Examination of stakeholder issues indicated that issues that are common to non-PPP and PPP projects are more prevalent than PPP specific issues. In particular, issues related to tolling are dominant; moreover, toll affordability is extremely sensitive, and its severity is predictable based on affected area demographics and past toll escalation practices. The study provided insights about how megaprojects are shaped through actions of project sponsors as well as impacted and interested stakeholders. It also demonstrated how these projects become artifacts of aspiration for politically powerful figures. Lastly, it identified the main stakeholder issues and suggested a set of guidelines to assist future practitioners in developing better stakeholder involvement strategies, which should both enhance and legitimize megaprojects. / Ph. D.