Citizen science approaches provide opportunities to support ecosystem service assessments. To evaluate the recent trends, challenges and opportunities of utilizing citizen science in ecosystem service studies we conducted a systematic literature and project review. We reviewed the range of ecosystem services and formats of participation in citizen science in 17 peer-reviewed scientific publications and 102 ongoing or finished citizen science projects, out of over 500 screened publications and over 1400 screened projects. We found that citizen science is predominantly applied in assessing regulating and cultural services. The assessments were often performed by using proxy indicators that only implicitly provide information on ecosystem services. Direct assessments of ecosystem services are still rare. Participation formats mostly comprise contributory citizen science projects that focus on volunteered data collection. However, there is potential to increase citizen involvement in comprehensive ecosystem service assessments, including the development of research questions, design, data analysis and dissemination of findings. Levels of involvement could be enhanced to strengthen strategic knowledge on the environment, scientific literacy and the empowerment of citizens in helping to inform and monitor policies and management efforts related to ecosystem services. We provide an outlook how to better operationalise citizen science approaches to assess ecosystem services.