NACE Rev.2.1 is the classification of economic activities corresponding to ISIC Rev. 4 at European level. Though more disaggregated than ISIC Rev. 4, NACE Rev. 2.1 is completely in line with it and can thus be regarded as its European version. Since the national economic structures vary considerably, there are economic activities appearing in NACE Rev. 2.1 which are not of importance or do not occur in all Member States (e.g. categories referring to agriculture, mining and quarrying, manufacture of spacecraft, etc). The NACE Rev. 2.1 Regulation allows the Member States to use a national version derived from NACE Rev. 2.1 for national purposes. Such national versions must, however, fit into the structural and hierarchical framework laid down by NACE Rev. 2.1.