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.
In Europe all pilots of light aircraft, general aviation and commercial aircraft must comply with these regulations for their licenses, ratings, approvals or certificates. The document below contains these regulations.
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.
To continue reading see the pdf below: