Leiden City of Neighbourhood Knowledge: The project has a ‘citizen-led’ character that enables residents of Leiden to express which healthy & sustainable living environment issues are most important in their neighbourhoods and participate in citizen science activities that provide data and insights that can inform policy, planning and local actions. In doing so we seek to embed these activities in the Leiden City of Knowledge partnership, and expand them to encompass residents, neighbourhoods, existing grassroots initiatives, and civil society organisations, such that all are working collaboratively towards a sustainable, healthy living environment for all residents of the city.