Mainline Protestantism is one of four major movements within Protestantism; the other three are evangelical, fundamentalism, and Pentecostal. They grew rapidly during the Great Awakening from the 1740s to the 1940s and dominated religion in America even into the 1950's, but they have been shrinking in membership and are now down to about 26 million. Though Catholics have long outnumbered Protestants in general, mainline adherents are now outnumbered by evangelical and Pentecostal/charismatic Christians; only fundamentalism has a smaller following among Protestants.
Theologically they were generally evangelical in the 19th century, liberal or modernist in the early 20th century, and now generally favor Neo-orthodoxy. Theology is not a central concern, and they rarely engage in heresy trials. However all have been deeply divided in recent years by such issues as homosexuality. The Mainline churches founded many colleges, universities and divinity schools. They were leaders in many reform movements, ranging from anti-slavery to temperance to the Social Gospel and Civil Rights Movement. They are organizers and dominate the National Council of Churches.
Mainline Protestant churches in America include the United Methodist Church, the Evangelical Lutheran Church in America, The Episcopal Church, the Presbyterian Church (USA), the United Church of Christ, the Disciples of Christ, the American Baptist Churches, and some smaller churches. Notably, the largest American Protestant denomination, the Southern Baptist Convention, is not counted within this group; it is considered evangelical due to its conservative theology (though according to some sources such as the liberal Pew Research, two of its splinter groups—the openly-liberal Alliance of Baptists and the so-called "moderate" Cooperative Baptist Fellowship—are counted as mainline).
- Ahlstrom, Sydney E. A Religious History of the American People (1976; 2004) excerpt and text search; see A Religious History of the American People
- Balmer, Randall. Grant Us Courage: Travels along the Mainline of American Protestantism (1996) online edition
- Balmer, Randall, and Fitzmier, John R. The Presbyterians (1993). 274 pp. excellent survey by scholars
- Billingsley, K. L. From Mainline to Sideline: The Social Witness of the National Council of Churches (1991)
- Coalter, Milton J.; Mulder, John M.; and Weeks, Louis B., eds. The Mainstream Protestant "Decline": The Presbyterian Pattern. (1990). 263pp.
- Dorrien, Gary. The Making of American Liberal Theology: Imagining Progressive Religion, 1805–1900 (2001); The Making of American Liberal Theology: Idealism, Realism, and Modernity, 1900–1950 (2003);The Making of American Liberal Theology: Crisis, Irony, and Postmodernity, 1950–2005 (2006), the standard history of mainline theology
- Hutchison, William R. ed. Between the Times: The Travail of the Protestant Establishment in America, 1900-1960 (1990) excerpt and text search
- Marty, Martin E. "The Establishment That Was," Christian Century November 15, 1989, p. 1045. online
- Marty, Martin E. Modern American Religion, Volume 1: The Irony of It All, 1893-1919 (1997) excerpt and text search; Modern American Religion, Volume 2: The Noise of Conflict, 1919-1941 (1997) excerpt and text search; Modern American Religion, Volume 3: Under God, Indivisible, 1941-1960 (1999), excerpt and text search;the best historical overview
- Roof, Wade Clark, and William McKinney. American Mainline Religion: Its Changing Shape and Future (1990) excerpt and text search
- Tipton, Steven M. Public Pulpits: Methodists and Mainline Churches in the Moral Argument of Public Life (2008) excerpt and text search
- Wuthnow, Robert, and John H. Evans, eds. The Quiet Hand of God: Faith-Based Activism and the Public Role of Mainline Protestantism, (2002), 430 pp.; essays by scholars