This file provides the correspondence table between EUROSTAT NUTS3 classification and the adapted regional classification used by the RISIS-KNOWMAK project. This regional classification fits the structure of knowledge production in Europe and addresses some knowm problems of the NUTS3 classification, such as the treatment of large agglomerations, while remaining fully compatible with the EUROSTAT NUTS regional classification. This compatibility allows combining all KNOWMAK data with regional statistics (at NUTS3 level, 2021 edition) from EUROSTAT. More precisely, the classification includes EUROSTAT metropolitan regions (based on the aggregation of NUTS3-level regions) and NUTS2 regions for the remaining areas; further, a few additional centers for knowledge production, like Oxford and Leuven, have been singled out at NUTS3 level. The resulting classification is therefore more fine-grained than NUTS2 in the areas with sizeable knowledge production, but at the same time recognizes the central role of metropolitan areas in knowledge production. While remaining compatible with NUTS, the classification allows addressing two well-known shortcomings: a) the fact that some large cities are split between NUTS regions (London) and b) the fact that NUTS3 classification in some countries includes many very small regions, as in the case of Germany