The Presbyterian Church (USA), abbreviated PCUSA, is a mainline Protestant denomination in the United States. It is the largest Presbyterian denomination in the country, known for its progressive stance on doctrine and its ordaining of women and members of the LGBT community as elders and ministers. The Presbyterian Church (USA) was established with the 1983 merger of the Presbyterian Church in the United States, whose churches were located in the Southern and border states, with the United Presbyterian Church in the United States of America, whose congregations could be found in every state.

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.