The original initiative for its establishment was contained in a resolution of the General Assembly of Unitarian and Free Christian Churches in 1987. This led to the establishment of the Advocates for the Establishment of an International Organization of Unitarians, which worked towards creating the council. However, the General Assembly resolution provided no funding. The Unitarian Universalist Association 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. It had already granted membership to congregations in Adelaide, Auckland, the Philippines and Pakistan, and congregations in Sydney, Russia and Spain had applied for membership. Rather than admit congregations from all over the world, the UUA hoped that they would join a world council instead. The UUA thus became willing to provide funding for the council's establishment. As a result, the council was finally established at a meeting in Essex, Massachusetts, United States on 23–26 March 1995.
Principles and purposes
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:
liberty of conscience and individual thought in matters of faith,
UK: General Assembly of Unitarian and Free Christian Churches, 6,000 members
USA: Unitarian Universalist Association, 162,796
Reorganizing
Kosciol Unitarianski, 80 attendees and friends.
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. This action is taken with regret and the ICUU looks forward to welcoming Poland back into membership at the earliest possible date.
Provisional members
Churches and religious associations which have expressed their will to become members of the Council may be admitted as "Provisional Members" for a period of time, until the Council decides that they have shown their organizational stability, affinity with the ICUU principles and commitment to deserve becoming Full Members of the Council. Provisional Members are invited to Council meetings through a delegate but cannot vote.
Kenyan Unitarians
Emerging groups
According to the , Emerging Groups are "applicants that are deemed to be reasonable prospects for membership, but do not fulfil the conditions of either Provisional membership or Full Membership". These groups may be designated as Emerging Groups by the Executive Committee upon its sole discretion. Emerging Groups may be invited as observers to General Meetings. The current list of Emerging Groups after the last meeting of the Executive Committee is as follows:
Congo Unitarians
French Unitarians
—Hong Kong
*
Mexico
Associates
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. The application must be approved by the ICUU Council Meeting.
Unitarian or Universalist groups which are in contact but with no formal link to the ICUU