In this study -part of the ACT II Digimon project- we focus on how a monitoring system for subsurface CO2 storage can contribute to the societal embeddedness of CO2 storage projects, based on insights from case studies in four European countries: Norway, The Netherlands, Germany and Greece. With four case studies we provide insight into which societal requirements and characteristics concerning the monitoring of CO2 storage sites are found relevant by both the general public, stakeholders and CCS experts to enhance the societal embeddedness of CO2 storage projects. We used a mixed methods approach across the four countries. First, we conducted 45 semi-structured interviews with (local) stakeholders and CCS experts in four European countries to gain insight into stakeholder experiences and preferences with regard to CCS and CCS monitoring. Then we conducted an Informed Questionnaire to gain insight into the opinion of the general public at a national and local level. At the national level in four countries input of a minimum of 1000 respondents per country was received. For the Dutch, German, and Norwegian case studies, we were also able to survey an additional local sample of a minimum of 200 respondents per country. Based on the outcomes of the semi-structured interviews and the Informed Questionnaire, we were able to draw three narratives reflecting how a monitoring system for subsurface CO2 storage can contribute to the societal embeddedness of CO2 storage projects. The first narrative concerns the insurance of safety of operation and communication about safety. The second narrative is linked to uncertainties on the long-term storage and the potential of CO2 storage for climate change mitigation. Finally, the third narrative elaborates on how monitoring can contribute to the evaluation and development of regulatory frameworks.