The A documents form the foundation: here you can read more about the general requirements set for companies that wish to participate in the GMP+ certification scheme.
GMP+ A1 General Regulation (version 15-07-2017)
GMP+ A2 Definitions and Abbreviations (version 01-07-2018)
GMP+ A3 GMP+ Logo's and/or Trademarks (version 15-09-2016)
GMP+ A4 Disputes Procedure (version 05-02-2018)
GMP+ A5 GMP+ Feed Certification Scheme License Agreement (version 15-07-2017)
GMP+ A6 Trade Sanctions Policy (version 12-11-2019)
Previous version of the documents above can be consulted here.