Policy makers are increasingly relying on Earth Observation (EO) data to make decisions on mitigating and adapting to climate change. These decisions need to be 'evidence-based' and this requires complete confidence in EO-derived products. Although EO data is plentiful, it is rare to have reliable, traceable and understandable quality information. The situation is often further confused because various versions of the same product exist from data providers using different retrieval algorithms.Users need an internationally acceptable Quality Assurance (QA) framework that establishes, and provides understandable traceable quality information for the data products used in Climate Services. This will ensure that long-term data sets are historically linked and, in the future, automatically harmonised in an efficient and interoperable manner.The Quality Assurance for ECVs (QA4ECV) project will address these issues by developing a robust generic system for the QA of satellite and in-situ algorithms and data records that can be applied to all ECVs in a prototype for future sustainable services in the frame of the GMES/Copernicus Climate Change Service. Multi-use tools and SI/community reference standards will be developed. The QA4ECV project will generate quality-assured multi-decadal Climate Data Records for 3 atmospheric ECV precursors (NO2, HCHO, and CO) and 3 land ECVs (albedo, LAI, and FAPAR), with full uncertainty metrics for every pixel ready for model ingestion. The generic QA framework will be applied to these ECVs. QA4ECV will engage with all stakeholders, including other ECV projects, governance bodies and end-users, developers of Climate Services and relevant projects.The QA4ECV project will show how trustable assessments of satellite data quality and reliable means of interoperability can facilitate users in judging the fitness-for-purpose of the ECV Climate Data Record. QA4ECV will be a major step forward in providing quality assured long-term Climate Data Records that are relevant for policy and climate change assessments.