Most countries are member of the International Civil Aviation Organization (ICAO) and as such have signed the "Chicago Convention 1944" (111 pages, 2 Mb). Aviation rules and regulations in member countries are based on the recommendations of the ICAO.
From the document: "COMMISSION REGULATION (EU) No 1178/2011 of 3 November 2011 laying down technical requirements and administrative procedures related to civil aviation aircrew pursuant to Regulation (EC) No 216/2008 of the European Parliament and of the Council".
Excerpt from the document:
This Regulation lays down detailed rules for: (a) different ratings for pilot licenses, the conditions for issuing, maintaining, amending, limiting, suspending or revoking pilot licenses, the privileges and responsibilities of the holders of pilot licenses, as well as the conditions for the conversion of existing national pilot licenses and of national flight engineer licenses into pilot licenses.
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