Many greenhouse gas mitigation actions also benefit air quality and health but assessment of these co-benefits has been limited. Over the next several years, C40 Cities will be working with city governments to develop climate action plans. They will integrate a screening-level air quality model focusing on particulate matter into C40’s climate action planning tool, Pathways, for at least three pilot cities. They will test the tool to explore air quality and health co-benefits of climate action pathways. We will also assess the potential for quantifying additional health co-benefits, such as changes in ozone, nitrogen dioxide levels, physical activity, noise and green space. Data and tools will be publicly available to support additional research into links between climate and health. Their work will build a bridge between scientific evidence on co-benefits to the largest urban climate action planning effort worldwide. Pathways will create a platform to study more cities and enable long-term integration of health co-benefits into climate action planning in cities.