The Unicode Standard is governed by a consortium of major American computer manufacturers. The ISO-10646 Standard is another universal character set standard governed by the International Organization for Standardization (ISO). In 1991, the ISO Working Group responsible for ISO-10646 standard and the Unicode Consortium agreed to work together to create a single universal standard for coding multilingual text. From Version 1.1 on, Unicode has been kept compatible with ISO-10646 and its extensions.

The ISO-10646 Standard defines two character encoding forms for representing characters in the universal character set (UCS):

UCS-2 is a fixed width subset of UTF-16 that does not support surrogate pairs; UCS-4 is equivalent to UTF-32. (See Unicode Character Encoding Forms.) Documentation for the Internationalization Module, including this manual, uses the Unicode Consortium terminology.