Air pollution, climate change, disease outbreaks and other threats have spurred a new form of public engagement with science and technology called environmental grassroots citizen science. Contrary to expert-led citizen science projects in which citizens collect scientific data for experts, these grassroots initiatives emanate from the bottom up, with citizens developing their own measurement tools and generating their own data, distinct from official institutional approaches. Environmental grassroots citizen science is markedly on the rise in Europe, where citizens demand policy action against air, traffic, and related forms of pollution. By taking science and technology into their own hands, citizens increase pressure on public authorities and scientists to ‘open up’ scientific research and environmental policymaking to society. Policymakers, scientists, businesses and other stakeholders are taking notice. Some experts express a willingness to work with these citizen scientists, while others raise concerns about the scientific quality of the data produced by citizens and the value these data have to those who set science policy, as most citizens lack formal scientific training. Grassroots citizen scientists in turn voice criticism of institutional science and its links with industry and government, arguing that such connections inhibit knowledge sharing and the development of a true participatory science culture. How then should we imagine environmental governance? What (if any) is the role of grassroots citizen science in this process? And how should governments and experts respond to citizen scientists and their demands? This research project seeks to develop answers to these questions in consultation with all concerned parties.This includes your. Your thoughts and suggestions will be shared with citizen scientists, decision makers, professional researchers, and others in a coordinated effort to identify and address the challenges and pitfalls of environmental governance.