A relatively young operational climate service is the Copernicus Climate Change Service (C3S, Thépaut et al. 2018), one of the six operational thematic services established by the European Commission within the Copernicus Earth Observation Programme (EC 2020). The C3S, implemented by the European Centre for Medium-Range Weather Forecasts (ECMWF), aims to be an authoritative source of climate information for a wide variety of downstream users, ranging from policy makers to industrial sectors. The backbone of C3S is a cloud-based Climate Data Store (CDS), designed to be a single point of access to a catalogue of climate datasets of different categories, including in-situ and satellite observations, seasonal forecasts, reanalysis, and climate projections. In a progressive commitment to establish relations of trust between data providers and downstream users, as well as providing sufficient guidance for users to address their specific needs, C3S has made significant investments in the development of an Evaluation and Quality Control (EQC) function. By being transparent and characterising data quality attributes in a traceable and reproducible way, C3S is setting the basis for the inclusion of reliable climate data into policies and actions. 4 Lacagnina et al.