The ESOTC 2021 report includes a short overview of the global context during the year, a more comprehensive overview of conditions in Europe, and a focus on the Arctic. It provides a detailed analysis, with descriptions of climate conditions and events, and explores the associated variations in key climate variables from across all parts of the Earth system. The ESOTC 2021 relies largely on datasets provided operationally and in near real-time by the Copernicus Services, to give an overview of 2021 in the long-term context. Data and reports from other monitoring activities are also included, when this has been considered informative and complementary.