ISO/IEC 646

ISO/IEC 646, is an ISO/IEC standard in the field of character encoding. It is equivalent to the ECMA standard ECMA-6 and developed in cooperation with ASCII at least since 1964. The first version of ECMA-6 had been published in 1965, based on work the ECMA's Technical Committee TC1 had carried out since December 1960. The first edition of ISO/IEC 646 was published in 1973, and the most recent, third, edition in 1991.

ISO/IEC 646 specifies a 7-bit character code from which several national standards are derived. It allocates a set of 82 unique graphic characters to 7-bit code points, known as the invariant (INV) or basic character set, including letters of the ISO basic Latin alphabet, digits, and some common Englishpunctuation. It leaves 12 code points to be allocated by conforming national standards for additional letters of Latin-based alphabets or other symbols.

It also defines the International Reference Version (IRV), including a full allocation of 94 graphic characters, to be used when a specific national version is not required. As of the 1991 edition of ISO/IEC 646, the IRV and ASCII are identical. Previous editions differed in only one or two code points.