The Chinese Character Code for Information Interchange (CCCII), developed in Taiwan in 1980, contains characters for use in China, Taiwan, and Japan. In somewhat modified form, it has been adopted for use in the United States as ANSI Z39.64-1989, also known as the East Asian Character Code (EACC) for bibliographic use. In 1981, Takahashi Tokutaro of Japan's National Diet Library proposed standardization of a character set for common use among East Asian countries.

The Unicode Han character set began with a project to create a Han character cross-reference database at Xerox in 1986. In 1988, a parallel effort began at Apple based on the Research Libraries Group's CJK Thesaurus, which is used to maintain EACC. The merger of the Apple and Xerox database led to the first draft of the Unicode Han character set in 1989. The Unicode Working Group proposed this set for inclusion in ISO 10646 at the September 1989.

The Unicode Han character set extended the bibliographic sets to guarantee complete coverage of industry and newer national standards. The unification criteria employed in this original Unicode Han character repertoire were based on rules used by JIS and on a set of Han character identity principle (rentong yuanze) being developed in China by experts working with the Association for a Common Chinese Code (ACCC).

The October 1989 meeting in Beijing was the beginning of informal cooperation between the Unicode Working Group and the ACCC to exchange information on each group's proposals for Han unification. A second ad hoc meeting on Han unification was held in Seoul in February 1990. Just at this meeting, the Korean delegation proposed the establishment of a group composed of the East Asian countries and other concerned organizations to study a unified Han encoding. From this informal meeting emerged the Chinese/Japanese/Korean Joint Research Group (CJK-JRG). And then, the December 1990 draft of the Unicode Han character set differed from the first draft in that is used the principle of KangXi radical-stroke ordering of the characters.

In the meantime, China announced that it was about to complete its own proposal for a Han Character Set, GB 13000. Concluding that the two drafts were similar in content and philosophy, the Unicode Consortium and the Center for Computer and Information Development Research, Ministry of Machinery and Electronic Industry (CCID, China's computer standards body) agreed to merge the two efforts into a single proposal. As a result of the agreement to merge the Unicode Standard and ISO 10646, the Unicode Consortium agreed to adopt the unified Han character repertoire that was to be developed by the CJK-JRG.

The first CJK-JRG meeting, held in Tokyo in July 1991, recognized that there was a compelling requirement for unification of the existing CJK ideographic characters into one coherent coding standard. Two basic decisions were made: to use GB 13000 as the basis for what would be termed "The Unified Repertoire and Ordering", and to verify the unification results base on rules.

On March 27, 1992, the CJK-JRG completed the Unified Repertoire and Ordering (URO), Version 2.0. This repertoire was subsequently published both by the Unicode Consortium in The Unicode Standard, Version 1.0. Volume 2 and by ISO in ISO/IEC 10646-1:1993.

In October 1993, the CJK-JRG became a formal subgroup of ISO/IEC JTC1/SC2/WG2 and was renamed the Ideograph Rapporteur Group (IRG). The Unicode Consortium participates in this group as a liaison member of ISO. The second meeting in Hanoi in February 1994, the IRG agreed to include Vietnamese Chu Nom ideographs in a future version of the URO and to add a fifth reference dictionary to the ordering scheme.

In 1998, the IRG completed the work on the first supplement to the URO, the CJK Unified ideographs Extension A. This set of 6,582 characters is culled from national and industrial standards and historical literature and is encoded in The Unicode Standard, Version 3.0. And then, It was published by ISO in ISO/IEC 10646-1:2000. Now, the IRG is considering additional CJKV ideographs submitted by China, Taiwan, Hong Kong, Japan, Korea, Singapore, and Vietnam as further extensions to the ideographic character repertoire in this standard.