The mainline (also sometimes called mainstream) or mainline Protestant denominations are those Protestant denominations with a mix of conservative, moderate, and liberal theologies. The hallmark of the mainline churches is moderation. Their theologies tend to be influenced by the Historical-critical method and culture at large, consciously or not. Ministers and members of mainline churches generally are comfortable with inclusive language translations of the Bible.
They tend to be open to new ideas and societal changes without abandoning what they consider to be the historical basis of the Christian faith. This places them to the left of the evangelical churches. They have been increasingly open to the ordination of women. They have been far from uniform in their reaction to homosexuals, bisexuals and transsexuals, though less dogmatic on these issues than either the Roman Catholic Church or the more conservative Protestant churches. Mainline churches take no set view with regard to military service — all provide chaplains to the United States armed forces and none are historically peace churches except the Church of the Brethren — but express reservations about aggressive use of military force for any reason.
Many or most mainline denominations teach that the Bible is God's word in function, but also remain open to new understandings of it. Few would suggest that the Bible was verbally and plenarily inspired as some biblical inerrantists maintain.
Most mainline denominations do not expect strict acceptance of everything written about or spoken by Jesus in the New Testament. Most are Trinitarian, however, meaning they accept and/or require belief in the doctrine that God exists as one "essence" in three "persons": the Father, the Son (Jesus Christ) and the Holy Spirit.
The term mainline may imply a certain numerical majority or dominant presence in mainstream society that is no longer accurate. The Association of Religion Data Archives (ARDA) counts 26,344,933 members of mainline churches versus 39,930,869 members of evangelical Protestant churches. There is evidence that there has been a shift in membership from mainline denominations to other churches.
The inclusion of a denomination in the mainline category does not imply that every member of that denomination, nor even every member of their clergy, accepts some of the beliefs generally held in common by other mainline churches. They allow considerable theological latitude. Moreover, mainline denominations have within them Confessing Movements or charismatic renewal movements which are more conservative in tone.
Some denominations with similar names, and historical ties to mainline groups are not considered mainline. For example, while the American Baptist Churches, the Evangelical Lutheran Church in America, and the Presbyterian Church (USA) are mainline, the Southern Baptist Convention, Lutheran Church - Missouri Synod, and the Presbyterian Church in America are Evangelical.
The Association of Religion Data Archives considers these denominations to be mainline:
The largest U.S. mainline churches are sometimes referred to as the Seven Sisters of American Protestantism.* The term was apparently coined by William Hutchison in reference to the major liberal groups of American Baptists, Disciples of Christ, Congregationalists / United Church of Christ, Episcopalians, Lutherans, Methodists, and Presbyterians during the period between 1900 and 1960.
The Association of Religion Data Archives has difficulties collecting data on traditionally African American denominations. Those churches most likely to be identified as mainline include these Methodist groups: