To understand what drives the concentration of CO2 in the atmosphere, it is crucial to understand the complexity of the underlying CO2 fluxes, and this first volume of FLUXES provides this information. FLUXES is a new publication designed to inform the interested audience of key scientific aspects of the European greenhouse gas budget. FLUXES will be published every summer to support the European Union in their preparation for the upcoming UNFCCC Conference of Parties and to guide European climate action in general. Greenhouse gas fluxes vary from year to year, that’s natural. However, Europe and the world are currently facing multiple hazards (heatwaves, droughts, fires, floods...) that are driven by climate change and – among many other damages – are altering greenhouse gas fluxes. These feedbacks put particularly natural CO2 sinks at risk but it requires monitoring of over long times to clearly identify and understand them. FLUXES, the European Greenhouse Gas Bulletin aims to transfer most recent scientific findings in order to distinguish occasional phenomena from long-term trends. It will focus on observations as the basis of a scientific value chain towards climate services and policy support.