Fortran provides tools to read and write both formatted (having a specification of how the data should be parsed for input, or presented for output) and unformatted (binary) data. File access can be sequential or random. The Fortran 2003 standard added streaming I/O. In this introduction we will only cover formatted, sequential I/O.

The read command is used for reading data. For writing data, the write command and the shorter print command (to write to standard output) can be used. The syntax of all three commands is very similar.