CLAiR-City aims at substantially improving future air quality and carbon policies in European cities by initiating new modes of engaging citizens, stakeholders and policymakers. The latest social science thinking will be applied to the source apportion of air pollution emissions and concentrations, carbon emissions and health outcomes in order to attribute them not just by technology but by citizens’ behaviour and daily activities. By putting people at the heart of both the problems and the solutions, we will stimulate the public engagement necessary to tackle our challenging emissions problems through the development of a range of citizen-led future scenario and policy packages. Using an innovative quantification and engagement toolkit to facilitate multi-stakeholder dialogue in six European pilot cities, the project will enable citizens and other stakeholders to discuss the role of air quality and carbon policies for citizens’ health, well-being and integral future quality of life. The results of this dialogue and engagement process will be evaluated and provide policy lessons on city, national and EU levels. The toolkit itself will be developed for targeting all EU cities with more than 50,000 citizens.