In this synthesis article, I discuss the meaning of active citizenship for European nature conservation based on an integrative study of existing literature. Four main knowledge gaps are addressed: (1) a lack of overview on the scope and characteristics of active citizenship across Europe; (2) a lack of systematic evidence on its impacts; (3) a lack of congruence in democratic debates related to active citizenship; and (4) the governance implications of active citizenship in context of these knowledge gaps. Empirical research shows that active citizenship is driven by a wide range of motivations and manifests in various forms. Although most active citizenship is small in scale, when added together all these groups of citizens have become a societal force to be reckoned with. Locally, active citizenship often provides important benefits to people and nature and also enriches the democratic system. However, active citizenship does not always align with policy frameworks and ecological networks and also leads to tensions between representative and direct forms of democracy. For these reasons, active citizenship should be considered as additive to other forms of governance in European nature conservation. In this, a polycentric and collaborative approach to green space governance can help authorities in achieving their own policy objectives while stimulating active citizenship.