ICOS, the Integrated Carbon Observation System, is a European-wide greenhouse gas research infrastructure: ICOS produces standardised data on greenhouse gas concentrations in the atmosphere, as well as on carbon fluxes between the atmosphere, the ecosystems, and the oceans. This ICOS-based knowledge supports policy and decision-making to combat climate change and its impacts. The high-quality ICOS data is based on the measurements from over 170 observation stations – run by top universities and research institutions across 16 European countries – and produced by the roughly 800 scientists in the community. The ICOS Carbon Portal offers unlimited access to thousands of datasets and other advanced digital products and services. ICOS has the status of an ERIC, European Research Infrastructure Consortium, with a legal capacity recognised in all countries within the European Union. FLUXES is a yearly publication by ICOS which aims at highlighting climate issues to an audience of policymakers, policy advisors, and climate journalists. The first volume was published in 2022. In this issue the following topics are highlighted around the central topic Monitoring,, Reporting and Verification (MRV) of greenhouse gas emissions: - A critical tool for tracking climate action progress - The truth is in the atmosphere - Successes and challenges when employing MRV - Timely and reliable data is crucial for EU policymaking - Tracking methane emissions: Making visible what is invisible - Assessing the progress, ambitions and challenges of the Global Stocktake - Transforming climate change mitigation accountability