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, and the OpenMP Application Program Interface v2.5 specification.
In the future, the GNU Fortran compiler may also support other standard variants of and extensions to the Fortran language. These include ISO/IEC 1539-1:2004 (Fortran 2003).