Earthwatch is one of the largest global backers of citizen-science--supported environmental research. For over forty years, Earthwatch has delivered a unique citizen-science model to empower individuals, students, teachers and corporate fellows to contribute to critical field-research to understand nature’s response to change. Earthwatch’s work supports hundreds of PhD researchers across dozens of countries, conducting over 100,000 hours of research annually. Earthwatch’s mission is to engage people worldwide in scientific field-research and education to promote the understanding and action necessary for a sustainable environment. To achieve its mission, Earthwatch works with multiple partners, universities, schools, businesses and other environmental organisations, to develop robust and impactful ‘citizen science’ programmes that contribute to valuable ecological challenges while providing an engaging experience for individuals that builds commitment for environmental action. Earthwatch has centred its activities on research in marine, freshwater, and terrestrial ecosystems by training and engaging more than 20,000 citizen scientists, including thousands of teachers. Earthwatch’s scientific team comprises seventeen scientists with experience in national (NERC), European and international research programmes on citizen science, and ecosystem monitoring and management, for example as a partner in the EU H2020’s projects MICS, this project (EU-Citizen.Science), Cos4Cloud, MONOCLE and Ground Truth 2.0. Earthwatch scientists participate in citizen-science--focussed working groups (COST Action CA15212 on citizen science) and regularly organise and contribute to international conferences (ECSA’s 2016, 2018 and 2020; CSA’s 2017 and 2019), events and workshops (World Water Week 2017, 2018 and 2019) to promote and improve citizen science.