Denominationalism is the division of a religion into separate religious denominations. The term is particularly used about the various Protestant schools of thought. Some groups of such denominations are

• The Presbyterians
• The Methodists
• The Anglicans
• The Lutherans
• The Baptists

Some denomination-type groups do not view themselves as such. Examples include

• The Church of Christ (may be more a "communion" than a denomination)
• The Eastern Orthodox churches (may be more a "communion" than a denomination)
• Churches of the Catholic Communion, most notably the Roman Catholic Church

Many Christians view denominationalism as a regrettable fact. The current trend as of 2005 is that the divisions are becoming less sharp, and there is an increasing cooperation between denominations. (See denomination for a distinction between denomination and association in religious governance.)

For an American example, despite historically deep differences in their respective theologies, few lay members of the United Methodist Church and the United Presbyterian Church could give an account of what those differences are. It is likely that laypeople from one denomination who attended a worship service of the other would find themselves in a mostly familiar environment. A far deeper divide, one that encompasses theological, cultural, and language differences, divides the neo-evangelical members of the Confessing Church movement in either denomination from the adherents of liberal Christianity. This division, though, exists in both denominations; and it is likely that members on either side of the inter-denominational line would have more in common with their counterparts in the other than they do with those on the other side of that line within the same denomination.

Theological denominationalism ultimately denies reality to any apparent doctrinal differences among the "denominations", reducing all differences to mere matters de nomina--"of names".

A denomination in this sense is created when part of a church no longer feel they can accept the leadership of that church as a spiritual leadership due to a different view of doctrine or what they see as immoral behaviour, but the schism does not in any way reflect either group leaving the Church as a theoretical whole.

This particular doctrine is, of course, unacceptable to those Christian groups that see themselves as being the "One Holy Catholic and Apostolic Church" as a whole. This includes the Eastern Orthodox, the Roman Catholics, and the Oriental Orthodox Communion, each of which claims to be the exclusive "Holy, Catholic, and Apostolic Church". In these denominations, it is not possible to have a separation over doctrinal or leadership issues, and any such attempts automatically are a type of schism.