Members of non-denominational churches often consider themselves simply "Christians", and many feel at home when visiting any number of other denominational churches with compatible beliefs.

On the other hand, some non-denominational churches consciously reject the idea of a denominational structure as a matter of doctrine, insisting that each congregation must be autonomous, sometimes pointing out that in early Christianity, there were no denominations. In support of this stance, 1 Corinthians 1:12-13,Pg.1439; King James Version is often cited. It reads:

“ Now this I say, that every one of you saith, I am of Paul; and I of Apollos; and I of Cephas; and I of Christ. Is Christ divided? was Paul crucified for you? Or were ye baptized in the name of Paul? ”

In essence, it can be said that each non-denominational church forms its own unofficial and unnamed "denomination" with a specific set of tenets as defined by the governing structure of the church (including its members). Any similarities between those beliefs and the beliefs of denominations or other non-denominational churches is entirely unintentional.

History

Non-denominational Christian churches are almost exclusively derived from the Protestant movement, as a fundamental part of Catholicism is visible organizational unity.

This is not to say that the visible unity of the Church was not an important doctrine of the Protestant Reformation. The Reformers of the 16th century Magisterial Reformation believed that they were reforming the Church Catholic. Each of them took very seriously the charges of schism and innovation, denying these charges and maintaining that it was the medieval church that had left them. Because of this the fundamental Unity of the Church Catholic remained a very important doctrine in the churches of the Reformation. Dr. James Walker wrote in "The Theology of Theologians of Scotland":

“ The visible church, 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.

Wherever the Reformation took place the result was not a new denomination but a reformation of a national church.

Denominationalism got its start 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 Church Catholic 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 Church Catholic 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 [citation needed]. Each denomination maintains to differing degrees some form of organizational and visible unity with its member churches, albeit radically decentralized compared with the Roman Catholic Church. Today, non-denominational 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.

In the United States, the number of evangelical non-denominational churches (often included in the category of American Protestantism) has increased exponentially since the late 1950s. Many historians of American religion cite after-effects of the Scopes Trial and baby boomers, as well as the higher standard of living available in the United States, and the movement away from authority in American culture due to Watergate and other scandals.

Other reasons of growth may include an increase want to focus on Jesus. Some people feel that belonging to a Christian denomination can pull focus off Christ and onto certain principles of the particular denomination which are not Christ. So growth may be caused by Christians (which literally means "partisans of Christ" or "of the household of Christ" who want to focus on Christ Jesus rather than denomination principles.

Non-denominational churches range from "simple" with only few members to "super" or "mega" churches of congregations of 1500+ attendees.

Common traits and tenets
While all non-denominational churches will differ to some degree, there are a number of aspects that are common to almost all of them.

Because they do not look to any human organization for doctrine, non-denominational churches generally claim the basic tenet of sola scriptura, that the bible alone is the source of doctrinal authority. From this, a number of similar doctrinal points can be found across most non-denominational churches, such as those found in the Nicene Creed and the Apostles' Creed. Individual churches differ in terms of how literally they interpret various texts of the bible.

Since most Christian non-denominational churches stemmed from the Protestant movement, almost all of them hold to the five solas, which are solus Christus, sola scriptura, sola fide, sola gratia, and Soli deo gloria (to God alone be the glory).

Because the five solas are the main tenets of the Protestant faith, many non-denominational churches are Protestant churches. However, some non-denominational groups reject this term for etymological reasons, stating that they are not protesting anything.

Many non-denominational churches can also be considered evangelical, especially when it comes to how one may be saved. Often (though certainly not always), non-denominational churches are loosely Baptist in doctrine and often borrow from charismatic, Pentecostal, Calvinist or fundamentalist ideas and practices as well.

Outside of doctrinal areas, non-denominational churches are generally more accepting of people from various religious backgrounds and political views. Services are occasionally modeled after those of another denomination, but are also usually tailored to the preferences of the congregation, and can change drastically even from week to week.

Examples
The following organizations and institutions label themselves as non-denominational:

Open Bible Standard Churches - Pentecostal
Open Brethren - non-charismatic, of UK origin
Churches of Christ - associated with the Restoration Movement; known for sola scriptura and for a cappella worship
Newfrontiers - charismatic, of UK origin
Sovereign Grace Ministries - identifies itself as "Reformed Charismatic"
Vineyard Movement - evangelical/charismatic
Independent Fundamental Churches of America - association of conservative, independent churches
Calvary Chapel - mildly charismatic, originating in California
Gordon College (Massachusetts) - once linked with Gordon-Conwell Theological Seminary
While in general, these groups will not have formal legal ties between individual congregations and consider themselves non-denominational, 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 churches.

Criticism
One argument against non-denominationalism claims that the pastor or teacher at such a church often has no theological degree, and can become a leader of the church without any of the theological training that large denominations generally require (although not all large denominations have such a requirement). While this does not apply to every non-denominational church, those to which it does apply argue that maturity and knowledge are all that are required for leadership, not completing a course in seminary. Other counterpoints claim that it is possible to be as knowledgeable (or more) as a seminary student via private study alone because of the grace of Jesus Christ.

Other critics maintain that there is no such thing as a truly "non-denominational" church, that all churches adhere to a core set of beliefs in some form, just as denominational churches do, even if those beliefs are not as formalized as a named denomination, and even if that church's adherents form a single congregation. Counterpoints made against these criticisms state that the basis of a denomination is the association with practices and beliefs that are more "worldly-based" than "Godly-based," or, in other words, are adherant to traditions and practices as defined by human standards, despite the understanding that all traditions and practices involve human influence at some basic level.

The most basic criticism of non-denominationalism is the duality of its nature; while non-denominationalism may be an excellent move toward a more catholic and ecumenical church body, it may be used as a marketing ploy. This may be as simple as "tricking" some Christians into attending a church or college that does not share their beliefs, or it may be as subtle as a church or college calling itself "nondenominational" simply to increase attendance or enrollment, focusing on that quantitative response rather than the quality of community or education.