The REGREEN NbS Transition Handbook provides a comprehensive overview of the REGREEN project's key findings and outcomes, focusing on Nature-based Solutions (NbS) for urban sustainability in Europe and China. The handbook is structured into nine chapters, each addressing crucial aspects of NbS design, implementation and governance. Below is an overview of the chapters as outlined in the handbook: Introduction and Urban Living Labs (ULLs): Highlights the strategic positioning of Urban Living Labs (ULLs), serving as innovative testbeds in the Local and Regional Governments (LGR) for co-creating knowledge and fostering urban innovation. The REGREEN project showcased its crucial role as a catalyst for strategic developments, capacity building, and the design and implementation of NbS by local and regional public organisations. Nature-based learning and NbS: Emphasises the pivotal role of education in addressing urbanisation and climate change challenges. Developed by an interdisciplinary team, REGREEN's educational approaches are participatory and action-oriented, instilling an appreciation for nature and awareness of NbS among the younger generation. Urbanisation and Ecosystem Services (ES): Explores the relationship between urbanisation and ES in Europe and China, with a focus on NbS as an approach. The chapter advocates for effective policies and the leveraging of NbS, particularly green and grey built infrastructure, to enhance urban resilience. Urban Ecosystem Service Mapping and Modelling: Provides a comprehensive overview of existing datasets on urban ES, advocating for standardised, comparable data. The chapter offers actionable insights for policymakers and urban practitioners, stressing the integration of ES into urban planning and collaborative, interdisciplinary decision-making approaches. Wellbeing Values of NbS: Delves into the comprehensive exploration of the health and well-being values associated with NbS, emphasising the complex nature of assigning values to NbS, especially in the context of health and well-being. Different types of evidence contribute to robust arguments supporting the integration of NbS into policies and strategic decisions. Initiatives for Scaling Up NbS: It outlines three key outcomes within the REGREEN project, addressing distinct aspects of promoting and scaling up NbS: an Online Decision Support Tool, a Prospectus for NbS Business Investment, and a Start-Up Accelerator Programme. These initiatives converge on the core principles of informed decision-making, innovation promotion, and stakeholder empowerment. Nature based Urban Land Use Planning Approaches: Provides a comprehensive exploration of planning approaches in urban land use planning within the REGREEN project, with a specific focus on 'de-paving' and 're-greening' strategies, capacity building for NbS practitioners, and pioneering urban coastal resilience. Governance Contexts for NbS Implementation: Investigates how diverse cultural and historical governance settings lead to innovations in governance approaches for NbS. The concept of 'governing architectures' is introduced, emphasising the impact on NbS outcomes and intervention success. The REGREEN NbS Transition Handbook provides actionable insights, methodologies, and recommendations tailored for policymakers, practitioners, and educators. It stands as a valuable tool for navigating the complexities of NbS, encouraging the replication of effective strategies, and bridging the gap between research and practical application. Ultimately, the handbook contributes to the development of a comprehensive and sustainable NbS ecosystem.