Hamburg is the first German city to have developed a comprehensive green roof strategy, aiming to plant a total of 100 hectares of roof surface in the city in the coming decade, to deal with the challenges climate change, densification, biodiversity, and air quality. The strategy combines different policy instruments: incentives, public relations and regulation. The implementation process comprises an incentive programme about 3 Mill. Euro, combined with mandatory requirements and quality standards. A local communication campaign is to raise awareness and knowledge among important actors. In the context of the ongoing scientific support in the implementation of the strategy, the strategy is being assessed to identify success factors of- and barriers to the successful implementation. In the first, qualitative assessment it is found that the essence of the success of the green roof strategy lies in the comprehensive approach, with the three action points enhancing each other in a continuous process.