There is strong evidence that natural environments within urban areas, such as parks, woodlands, lakes and beaches, have positive impacts on health. These urban green and blue spaces (UGBS) could be huge assets for protecting and equalising health if they were available, accessible, valued and well-used, particularly by less advantaged groups. The problem is that they are not. This is largely because the many policies, organisations and communities involved in designing, creating, managing, promoting, maintaining and using UGBS are disconnected. Also, the voices of less advantaged communities that UGBS could be helping most are either not heard or not persuasive. Perhaps as a consequence, those communities are much less likely to benefit from these spaces. We know that the UGBS we have are not the UGBS we need to make the best possible contribution to better and more equal health. GroundsWell aims to change that. We propose a new partnership - researchers working together with communities and those who currently create and control UGBS, to plan, design and manage it better so that it benefits everyone, especially those who need it most. The main research will take place in three cities - Belfast, Edinburgh and Liverpool. These have sufficient similarities (such as large and diverse low-income communities) but also distinct features (such as geography and culture) making them, collectively, an ideal laboratory. Each city already has policies and programmes in place to improve UGBS, but there is much room for improvement. GroundsWell will take a systems approach. This means understanding the multiple and interconnecting components of policy-making, practice, perception and people which together affect the presence, location, character and use of UGBS. It also means working to transform the system so that the components function together. To do this, GroundsWell will mix co-development of new theoretical frameworks, novel data science including simulation, health economics and policy analysis, but at its heart will be community engagement and partnership. We will develop and use meaningful community engagement, co-production and citizen science to understand the system, identify how and where it is broken, and co-create solutions. We anticipate interventions aimed at how the UGBS system operates, and small-scale interventions around actual spaces and their use. Data play an important part in understanding systems. GroundsWell will develop an accessible, trustworthy and policy-relevant system to collate, collect, house and share data on UGBS across the three cities. These data will be used to help the whole Consortium understand the UGBS there, identify possible interventions, and then assess whether they work, for whom and why, creating feedback loops to help us continually monitor, learn and adapt what we do. Novel simulation approaches will also be used to suggest interventions, and in particular what could be effective beyond the three cities. Health economics will suggest what would be best value for money. An important part of putting actions and solutions in place is understanding if they work (or not). Evaluation of our actions and the Consortium as a whole will be undertaken in partnership with our communities, drawing on the new data system we establish, and enabling them to directly see whether and how the process has benefited them. In particular, we will assess and share our impacts on health inequalities. We are realistic about the likely scale of our impacts. Small actions within existing UGBS and local communities are unlikely to affect population level health and inequalities within our funded period. That is why we are going to focus on improving the UGBS system as a whole, laying foundations for long-term benefits. We know that the use and enjoyment of UGBS is something that adults pass on to their children. If GroundsWell can improve and equalise the role of UGBS, it will achieve a lasting impact.