Fortran is developed by the Working Group 5 of Sub-Committee 22 of the Joint Technical Committee 1 of the International Organization for Standardization and the International Electrotechnical Commission (IEC). This group is known as WG5. Official Fortran standard documents are available for purchase from ISO; a collection of free documents (typically final drafts) are also available on the wiki.
The GNU Fortran compiler implements ISO/IEC 1539:1997 (Fortran 95). As such, it can also compile essentially all standard-compliant Fortran 90 and Fortran 77 programs. It also supports the ISO/IEC TR-15581 enhancements to allocatable arrays.
GNU Fortran also supports almost all of ISO/IEC 1539-1:2004 (Fortran 2003) and ISO/IEC 1539-1:2010 (Fortran 2008). It has partial support for features introduced in ISO/IEC 1539:2018 (Fortran 2018), the most recent version of the Fortran language standard, including full support for the Technical Specification Further Interoperability of Fortran with C (ISO/IEC TS 29113:2012). More details on support for these standards can be found in the following sections of the documentation.