The main objective of WP1 is to assess and document the priority needs of official (national) inventory-preparing institutions to establish policy-relevant observation-based GHG budgets estimation methods that will be prototyped in WPs 2 to 4. This WP will provide the needed link and dialogue to address the policies and StockTake process from the Paris Agreement for the three GHGs with the common involvement of inventory agencies and research groups participating to the project. WP1 will connect to other WPs through: i) the assessment of the current UNFCCC MRV framework and its future evolution, e.g. to address the recommendations produced in 2019 by the IPCC Task Force on National GHG Inventories14 and ii) a careful and detailed analysis of uncertainties in National inventories with respect to the main needs and gaps per country, sector, gas, establishing regular interactions between the different communities. WP1 will contribute to the delivery of Product 4 with WP6.