In European urban development practices, there is a recurring need for new perspectives that provide insight into the complexity involved in the realization of projects. This need exists particularly around prestigious projects, where the tension between planning ambitions on the one hand, and the reality of conflicting interests and tight budgets on the other reaches its highest point. In the Netherlands, it is also likely that this tension will not decrease in the coming years. Reason enough for an investigation into strategies for urban development projects. This thesis combines several existing scientific insights around the phenomenon 'strategy'. Here, strategy is recognized as force. The term force emphasizes that a strategy, as opposed to a plan, provides those involved with the capacity to respond to the continuously changing reality of an urban development project. Thus, an effective strategy not only consists of making plans, but also includes three other strategic activities: venturing, learning, and visioning. These insights are then specified on the basis of the remarkable case of Rotterdam CityPorts – a project between city and port in which political and economic forces are especially amplified. This leads the thesis to develop a comprehensible theoretical model that reflects the complexity occurring in the realization of contemporary urban development projects. This strategy-as-force model is useful for both scientists and practitioners.