Trees and forests are a proven nature-based solution that contribute to sustainable urban development. Their potential for delivering ecosystem services, enhancing biodiversity and contributing to the wellbeing of urban societies is often underestimated and underused. CLEARING HOUSE provides evidence and tools that facilitate mobilising the full potential of urban forests as nature-based solutions (UF-NBS) for rehabilitating, reconnecting and restoring urban ecosystems. UF-NBS comprise every measure a city can take to address urban development challenges by deploying tree-based ecosystems. CLEARING HOUSE will review existing knowledge and will collect new data from large scale analyses (WP1), and evidence emerging from the comparative analysis of ten case studies in Europe and China (WP2), including a citizen science approach. Knowledge will relate to the social, economic and policy drivers of UF-NBS, their design and implementation, and their impacts on urban ecosystem and human wellbeing across continents. CLEARING HOUSE implements a co-design approach early in the project to ensure that its research programme exactly fits the demand of end-users, and engages stakeholders and scientists in problem-oriented knowledge generation through a set of targeted learning mechanisms (WP3). CLEARING HOUSE then develops user-targeted outputs to support cities, planners, business and civil society in implementing UF-NBS. Inter alia, decision support tools such as an online application, a global benchmarking tool and guidelines will provide knowledge on the design, governance and management of UF-NBS, and on sustainable business models relating to them (WP4). Target group specific communication and dissemination activities complement the project. These include Sino-European science-policy symposia (WP5) targeting senior decision-makers, activities targeting businesses and civil society organisations, and measures reaching out to citizens including school children (WP5).