The ISO Standard for Fortran90 has, officially, replaced that for Fortran77. It introduces a wealth of new features many of them already in use in other high-level languages, which will make programming easier, and facilitate the construction of portable and robust programs. The whole of the Fortran77 Standard is included as a proper subset, so existing (standard-conforming) Fortran programs will automatically conform also to the new Standard. Until well-tested compilers for Fortran90 are widespread, however, most programmers are still using Fortran77, with perhaps a few minor extensions.