Managing spatial development projects projects is a challenge because they are technically complex, take place in a dynamic environment and many stakeholders are involved. To successfully manage these projects a combination of project management and process management is required. Main research question is: How can managers of spatial development projects, given the context and management issues in these developments, properly apply project-oriented and process-oriented interventions and by that increase the success of their management? Project managers can influence the success of their project by applying interventions that match the current project situation. It is possible to distinguish elements of a project situation that require project management and elements that require process management. However, a project situation is almost never purely suited for project management or purely suited for process management. Therefore in many interventions aspects of project and process management have to be combined. There are several mechanisms to combine project and process management by interventions. Based on this research, three recommendations are formulated: 1. It is recommended to actively search for “windows of opportunity”, which offer the perfect opportunity to successfully apply a specific intervention. 2. To intervene successfully in ambiguous project situations, interventions should contain a combination of project and process management. It is recommended to weave project and process management together in an individual intervention or in a series of linked interventions. 3. Three intervention mechanisms are identified to combine project and process management. First, it is recommended to let project and process management contribute to each others objectives with the appliance of mutually reinforcing interventions. Second, it is recommended that potential negative effects of interventions are compensated by adding project-oriented conditions to process-oriented interventions and by adding process-oriented conditions to project-oriented interventions. Third it is recommended to apply project and process management interventions based on each other's results.