The Christian Church (Disciples of Christ) is a mainline Protestant Christian denomination in the United States and Canada. The denomination started with the Restoration Movement during the Second Great Awakening, first existing during the 19th century as a loose association of churches working towards Christian unity, then slowly forming quasi-denominational structures through missionary societies, regional associations, and an international convention. In 1968, the Disciples of Christ officially adopted a denominational structure at which time a group of churches left to remain nondenominational.

The mainline Protestant churches are a group of Protestant denominations in the United States and in some cases in Canada largely of the theologically liberal or theologically progressive persuasion that contrast in history and practice with the largely theologically conservative Evangelical, Fundamentalist, Charismatic, Confessional, Confessing Movement, historically Black church, and Global South Protestant denominations and congregations. Some make a distinction between "mainline" and "oldline", with the former referring only to denominational ties and the latter referring to church lineage, prestige and influence. However, this distinction has largely been lost to history and the terms are now nearly synonymous.