Central to integrated flood risk management is the integration of water management with spatial planning. Existing studies often focus on analyzing the policy instruments in the initiation and planning phases of integrated flood risk management. Little is known, however, about the policy instrument mixes that enable implementation of integrated flood risk management. Therefore, in this article we analyze the Dutch Room for the River program to identify what mixes of policy instruments enable successful integrated flood risk management in the implementation phase. We collected archival and survey data and analyzed 19 implemented projects in the Room for the River program applying Qualitative Comparative Analysis (QCA). We conclude that no single policy instrument is necessary or sufficient for successful implementation. We found three policy instrument mixes: an integrated contract mix, a project management mix, and an outside-government mix.