Unitarian Universalism formed in 1961 through the merger of American Unitarianism and Universalism, two historically distinct liberal Christian denominations that had each already moved, before their merger, toward increasingly noncreedal positions rejecting required doctrinal statements in favor of individual conscience and ongoing spiritual search, a founding principle that directly shapes why Unitarian Universalist congregations today draw on many different religious and secular sources for worship and prayer, including Christianity, Judaism, Buddhism, Hinduism, paganism, humanism and others, rather than following any single required theology or prayer tradition. This explicit institutional commitment to noncreedal pluralism, formalized in the denomination's own stated Principles and Sources, means Unitarian Universalist prayer practice genuinely varies from congregation to congregation and even from individual to individual within a single congregation, ranging from theistic prayer addressed to God, through non-theistic meditation or reflection, to invocations drawing on entirely secular or humanist language.
Unitarianism historically emphasized the oneness of God against Trinitarian doctrine, while Universalism emphasized the eventual salvation of all souls against doctrines of eternal damnation, two originally distinct theological arguments whose shared trajectory toward broader religious tolerance ultimately made their nineteenth and twentieth century convergence and eventual merger a natural institutional development.