The 1st CO4EO Workshop, entitled as “Citizen Science and Conventional Earth Observation”, took place within the 39th annual symposium of EARSeL, in Salzburg, Austria, on 2 of July 2019. The workshop, organised by the H2020 WeObserve project (www.weobserve.eu) brought out best practices from the crowdsourcing data capitalization in combination with earth observation data (through sensors) in order to improve monitoring of various environmental phenomena. During the workshop, the H2020 COs , GroundTruth 2.0, Scent, GROW and LandSense, presented their innovative applications as well as other tools developed within the lifetime of their projects in order to assist and improve environmental monitoring. Particular emphasis was given in the field of Land Use and Land Cover (LU/LC), harnessing the power of citizens to create actionable knowledge for participatory governance and policy making. In addition, potential solutions and promotion of policy adoption were discussed on overcoming limitations of citizen science data in Earth observation applications.