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Nondenominational (or non-denominational) Christian institutions are those not formally aligned with an established religious denomination, but are historically Protestant, or that remain otherwise officially autonomous. This, however, does not preclude an identifiable standard among such congregations. Nondenominational church congregations may establish a functional denomination by means of mutual recognition of or accountability to other congregations and leaders with commonly held doctrine, policy and worship without formalizing external direction or oversight in such matters. Some nondenominational churches explicitly reject the idea of a formalized denominational structure as a matter of principle, holding that each congregation is better off being autonomous. A 2012 Gallup survey reported that 10% of U.S. adults identify as non-specific Christian.
|“||The visible churches, in the idea of the Scottish theologians, is catholic. You have not an indefinite number of Parochial, or Congregational, or National churches, constituting, as it were, so many ecclesiastical individualities, but one great spiritual republic, of which these various organizations form a part. The visible church is not a genus, so to speak, with so many species under it. It is thus you may think of the State, but the visible church is a totum integrale, it is an empire. The churches of the various nationalities constitute the provinces of this empire; and though they are so far independent of each other, yet they are so one, that membership in one is membership in all, and separation from one is separation from all... This conception of the church, of which, in at least some aspects, we have practically so much lost sight, had a firm hold of the Scottish theologians of the seventeenth century.||”|
In some countries where the Protestant Reformation took place, the founders claimed that the result was not a new denomination but a reformation of a supposedly pre-existing "national" church.
Denominationalism was accelerated in the aftermath of the Westminster Assembly convened by the English Parliament to formulate a form of religion for the national churches of England and Scotland. In the debate between the two main parties present at the Assembly, the Presbyterians and the Independents, the Presbyterians were in favor of a form of church government that maintained the visible organizational unity of the Catholic Church while Independents, weary of the ecclesiastical tyranny they experienced under the Episcopal system, wished to organize the churches in a congregational way envisioning no legitimate authority of the church above the local congregation meeting at one time in a single place. Obviously these two parties were not reconciled and following the Assembly the Independents formed their own independent church. Thus instead of a united expression of the Catholic Church in England there were now two churches.
Protestant denominations spread and multiplied, especially in the United States, as Denominational confessional statements began to be used more to exclude than to include Christians with different doctrinal convictions. Each denomination maintains to differing degrees some form of organizational and visible unity with its member churches, albeit radically decentralized compared with the Catholic Church.
Today, nondenominational churches, like the Independents at the Westminster Assembly, refuse to recognize any ecclesiastical authority above the local congregation and deny the visible unity of the Church (though not the unity of the invisible Church) despite the fact that the original denominations were formed by substantially the same ideology.
Boston University religion scholar Stephen Prothero argues that nondenominationalism hides the fundamental theological and spiritual issues that drove the division of Christianity into denominations in the first place behind a veneer of "Christian unity". He argues that nondenominationalism encourages a descent of Christianity—and indeed, all religions—into comfortable "general moralism" rather than being a focus for facing the complexities of churchgoers' culture and spirituality. Prothero further argues that it also encourages ignorance of the Scriptures, which in turn reduces overall religious literacy, increasing the potential for inter-religious misunderstandings and conflict.
Fr. Jonathan A. Mitchican, a traditional Anglican priest, has also argued that the term non-denominational is essentially misleading: "If an American church calls itself “non-denominational,” nine times out of ten what that means is Baptist. Altar calls and appeals to personal conversion replace the sacraments as the means of grace. Baptism is a symbol of one’s personal conversion, nothing more, and it is only appropriate for adults", theological positions that are at odds with what Anglicans, and Christians outside of the modern United States, have generally believed. 
The following organisations and institutions label themselves as nondenominational:
- Bread of Life Ministries International—nondenominational megachurch in Manila, Philippines. Church's mission and vision is love for God and sharing the Gospel are strongly linked to patriotism; emphasises both the spiritual kingdom and nation-building
- Brunstad Christian Church—claims to differ from other nondenominational groups in its belief that Jesus was tempted to sin like every human being
- Bible church 
- Calvary Chapel—mildly charismatic, originating in California
- Christ's Commission Fellowship—nondenominational megachurch in the Philippines, they focus on being "Christ-Committed Followers"
- Christian Congregation in the United States—self-declared nondenominational and non-sectarian
- Churches of Christ in Christian Union—focuses on free-form worship and evangelism
- Churches of Christ—associated with the Restoration Movement; known for sola scriptura, a cappella worship, and baptism for the forgiveness of sins
- Christian churches and churches of Christ - also associated with the Restoration Movement; unlike the Churches of Christ, the Christian Churches and instrumental Churches of Christ use instruments otherwise both denominations are the same thing.
- Christian Worship Center
- Crossroads Christian Church
- Cornerstone Fellowship—a nondenominational church in Livermore, California
- Evangelical Christian Church in Canada (Christian Disciples)
- Family Stations, Inc.—identifies as a nondenominational, Christian radio ministry
- Gordon College (Massachusetts)—started by a Baptist church. Formerly part of Gordon-Conwell Theological Seminary
- International Churches of Christ—also associated with the Restoration Movement. Founded by Kip Mckean
- International Christian Churches—separated from the International Churches of Christ, 2006 in Portland, Oregon. Also founded by Mckean
- Independent Fundamental Churches of America—association of conservative, independent churches
- Jesus Is Lord Church—charismatic, headquarters in Bocaue, Bulacan, Philippines. Headed by founder Bro. Eddie Villanueva, JIL started with 15 members in 1978. As of 2010, members are about 6 million
- Lakewood Church—non-denominational Christian megachurch located in Houston, Texas. It is evangelical and charismatic in belief, founded by John Osteen, and led by his youngest son, Joel Osteen, today.
- Local churches (Chinese: 地方教會)—a Chinese Christian movement influenced by the teachings of Watchman Nee and Witness Lee, associated with Living Stream Ministry
- Mars Hill Church—identifies itself as "Reformed, Charismatic, Missional, and Complementarian"
- Metro Life Church
- New Creation Church—charismatic, located in Singapore. Founded and led by Joseph Prince
- Newfrontiers—charismatic, originating in the United Kingdom
- Open Bible Standard Churches—Pentecostal
- Open Brethren—non-charismatic, originating in the United Kingdom
- Plymouth Brethren
- People of Praise-charismatic non-denomenational covenant community. Self-identified as a Christian ecumenical charismatic covenant community. Members maintain active status in various churches and denominations. Unaffiliated with any church or denomination. A majority of its members are also practicing Catholics. Originating in the United States.
- Sovereign Grace Ministries—identifies itself as "Reformed Charismatic"
- Victory Christian Fellowship—megachurch in the Philippines under the Every Nation Ministries
- Vineyard Movement—evangelical/charismatic
- The Way International—non-Trinitarian
- World Changers Church International—originating in College Park, Georgia
While many of these groups will not have formal legal ties between individual congregations and consider themselves nondenominational, outsiders often describe them as denominations in and of themselves due to their close associations, equivalent doctrine, similar worship practices, and the ease of using one name to cover a larger group of ecclesial communities.
- "Religion". Gallup. 2012.
- Note that in this quotation the word "catholic" is used in the sense of "universal." Dr. James Walker in The Theology of Theologians of Scotland. (Edinburgh: Rpt. Knox Press, 1982) Lecture iv. pp.95–6.
- Prothero, Stephen (2007). Religious Literacy: What Every American Needs to Know - and Doesn't. New York: HarperOne. ISBN 0-06-084670-4.
- "Ask an Anglican: An Evangelical, a Baptist, and a Charismatic Walk Into a Bar…".