The Horizon 2020 project, LandSense, is a modern citizen observatory for Land Use & Land Cover (LULC) monitoring, that connects citizens with Earth Observation (EO) data to transform current approaches to environmental decision making. Citizen Observatories are community-driven mechanisms to complement existing environmental monitoring systems and can be fostered through EO-based mobile and web applications, allowing citizens to not only play a key role in LULC monitoring, but also to be directly involved in the co-creation of such solutions. Within LandSense, citizens can participate in ongoing demonstration pilots using their own devices (e.g. mobile phones and tablets), through interactive reporting, gaming applications and mapathons. Campaigns in Vienna, Toulouse, Amsterdam, Serbia, Spain and Indonesia address topics such as urban greenspaces, agricultural management and biodiversity/habitat threat monitoring. For example, in the case of Toulouse and Indonesia, hotspots of change in LULC are identified through Sentinel 2 time series analysis. These hotspots are then validated by citizens and interested stakeholders either directly on-site via customized mobile applications, providing geotagged photos, or remotely via the online LandSense Engagement platform. The presentation will not only showcase the tools and results from these campaigns, but also highlight how citizen-driven observations can contribute to sustainable development. Such initiatives present clear opportunities to integrate citizen-driven observations with established authoritative data sources to further extend GEOSS and Copernicus capacities, and support comprehensive environmental monitoring systems. In addition, these applications have considerable potential in lowering expenditure costs on in-situ data collection and current calibration/validation approaches within the processing chain of environmental monitoring activities both within and beyond Europe.