[1] Some groups represented only a few hundred people; while the largest, the Unitarian Universalist Association, had more than 160,000 members as of May 2011[update]—including over 150,000 in the United States.

The Unitarian Universalist Association (UUA) became particularly interested in the establishment of a council when it had to deal with an increasing number of applications for membership from congregations outside North America.

As a result, the council was finally established at a meeting in Essex, Massachusetts, United States on 23–26 March 1995.

The Preamble to the Constitution of the International Council of Unitarians and Universalists reads: We, the member groups of the International Council of Unitarians and Universalists, affirming our belief in religious community based on: declare our purposes to be: Polish Unitarians have reported a need for a period of reorganization, and that at this time they are unable to maintain the level of activity needed to be full Council members, be it moved that membership of these groups be suspended.

The current list of Emerging Groups after the last meeting of the Executive Committee (London, 22–25 November 2008) is as follows: Organizations with beliefs and purposes closely akin to those of ICUU but which by nature of their constitution are not eligible for full membership or which do not wish to become full members now or in the foreseeable future, may become Associates of the ICUU.