Fortran is a general purpose programming language, mainly intended for mathematical computations in science applications (e.g. physics). Fortran is an acronym for FORmula TRANslation, and was originally capitalized as FORTRAN. However, following the current trend to only capitalize the first letter in acronyms, we will call it Fortran. Fortran was the first high-level programming language. The work on Fortran started in the 1950's at IBM and there have been many versions since. By convention, a Fortran version is denoted by the last two digits of the year the standard was proposed. Thus we have Fortran 66, Fortran 77 and Fortran 90 (95). The most common Fortran version today is still Fortran 77, although Fortran 90 is growing in popularity. Fortran 95 is a revised version of Fortran 90 which is expected to be approved by ANSI soon (1996). There are also several versions of Fortran aimed at parallel computers. The most important one is High Performance Fortran (HPF), which is a de-facto standard. Users should be aware that most Fortran 77 compilers allow a superset of Fortran 77, i.e. they allow nonstandard extensions. In this tutorial we will emphasize standard ANSI Fortran 77.