The construction industry gets increasingly aware of the importance and value of people. Considering the nature of construction projects a certain level of collaboration is needed to successfully deliver a project. Throughout the complete project life cycle of large engineering projects, multiple actors are involved. As in any other industry and if not more, it is crucial to understand how people work and collaborate. Collaboration is positively associated with project performance. This research is conducted, from a managing contractor perspective, to study the formation of a coalition in the construction phase of a large engineering project. The coalition consists of the client, the managing contractor, and subcontractors. The coalition members are critical in finishing the project. The project management intervention is implemented to increase collaboration between coalition members. It should lead to increased organizational effectiveness. However, it remains unclear what the effect of a coalition is. Moreover, it is unclear how people, groups, and the project organization are affected by this intervention...