Fortran Standards Documents
Draft (unofficial) versions of the various recent Fortran standards and corrigenda are available from the [http://j3-fortran.org/ J3 website], the [http://www.nag.co.uk/sc22wg5/ WG5 website], and/or the [ftp://ftp.nag.co.uk/sc22wg5/ WG5 file server], in various formats. In addition, some older Fortran standards are available from [http://www.fortran.com www.fortran.com].
Note that, of these standards, GNU Fortran currently only supports the base Fortran 95 standard (not parts 2 or 3) as amended in the two corrigenda, the Fortran 95 TR 15581 extension, the Fortran 77 standard, and some portions of the Fortran 2003 standard; these standards have been highlighted in bold. The other documents are linked here for reference, but should not be taken as documentation of GNU Fortran features.
Fortran 66 Standard (X3.9-1966): [http://www.fh-jena.de/~kleine/history/languages/ansi-x3dot9-1966-Fortran66.pdf (pdf)]
Fortran 77 Standard (X3J3/90.4): [http://www.fortran.com/fortran/F77_std/f77_std.html (text)] [http://www.fortran.com/fortran/F77_std/rjcnf.html (html)]
DoD Extensions to Fortran 77 (MIL-STD 1753): [http://www.fortran.com/fortran/mil_std_1753.html (html)]
Fortran 95 Standard, final draft (ISO/IEC 1539-1:1997): [http://j3-fortran.org/doc/standing/007%20Draft%20Revision%20to%20Fortran%20Standards%20Document/97-007r2/ (all formats)], [http://j3-fortran.org/doc/standing/007%20Draft%20Revision%20to%20Fortran%20Standards%20Document/97-007r2/pdf/97-007r2.pdf (pdf)].
Fortran 95 Standard (Part 2: ISO-Varying-Strings), final draft (ISO/IEC 1539-2:2000): [ftp://ftp.nag.co.uk/sc22wg5/N1351-N1400/N1375.pdf (pdf)]
Fortran 95 Standard (Part 3: Conditional Compilation), final draft (ISO/IEC 1539-3:1998): [ftp://ftp.nag.co.uk/sc22wg5/N1301-N1350/N1306.pdf (pdf)]
Fortran 95 Floating-Point Exceptions TR (TR 15580): [ftp://ftp.nag.co.uk/sc22wg5/N1351-N1400/N1378.pdf (pdf)]
Fortran 95 Allocatable Components TR (TR 15581): [ftp://ftp.nag.co.uk/sc22wg5/N1351-N1400/N1379.pdf (pdf)]
Fortran 95 Corrigendum 1: [ftp://ftp.nag.co.uk/sc22wg5/N1401-N1450/N1421.pdf (pdf)]
Fortran 95 Corrigendum 2: [ftp://ftp.nag.co.uk/sc22wg5/N1451-N1500/N1472.pdf (pdf)]
Fortran 2003 Standard, final draft (ISO/IEC 1539-1:2004(E)): [http://www.j3-fortran.org/doc/year/04/04-007.txt (ascii)], [http://www.j3-fortran.org/doc/year/04/04-007.tex.tar (TeX)], [http://www.j3-fortran.org/doc/year/04/04-007.pdf (pdf)].
Fortran 2003, Enhanced Modules TR (ISO/IEC TR 19767:2005(E)): [ftp://ftp.nag.co.uk/sc22wg5/N1601-N1650/N1602.pdf (pdf)].
Fortran 2003 Corrigendum 1: [ftp://ftp.nag.co.uk/sc22wg5/N1601-N1650/N1636.pdf (pdf)].
Other Relevant Standards
The IEEE standard covering Fortran 77 POSIX bindings is available online, though unfortunately only from locations with appropriate subscriptions to the IEEE server (e.g., many university networks). For those who do have such access, the link is:
POSIX Fortran 77 Language Interfaces (IEEE Std 1003.9-1992) [http://ieeexplore.ieee.org/iel1/2891/4710/00182910.pdf?isnumber= (pdf)]