FOR is an extension that is specific to files related to a general purpose multi-paradigm programming language called Fortran. FOR files are used to store the source code of a program written in that language. Technically, it is a plain text file that can be handled by any editor. However, FOR this type of file, tools that make it easier to work with the code are most often used.

FOR files are mainly known from the older Fortran 77 version.