(Previously "Fortran 8x" and "Fortran Extended") An extensive enlargement of Fortran 77. Fortran 90 has derived types, assumed shape arrays, array sections, functions returning arrays, case statement, module subprograms and internal subprograms, optional and keyword subprogram arguments, recursion, and dynamic allocation. It is defined in ISO 1539:1991, soon to be adopted by ANSI.

["Fortran 90 Explained", M. Metcalf et al, Oxford University Press 1990].