Throughout the 1960s, the Protestant mainline developed a theology of “responsible parenthood,” grounded in scripture and Christian thought that turned the use of contraception within marriage into a site of Christian moral agency. Responsible parenthood language offered religious responses to scientific advances and scientifically articulated social problems like population explosion. Protestant clergy, nationally and locally, deployed it to encourage birth control among married couples. These leaders were often members of what is called “mainline” Protestantism, encompassing such moderate, non-evangelical denominations such as the United Methodist Church, the United Church of Christ, the Presbyterian Church (USA), the American Baptist Church, and the Episcopal Church. They eschewed fundamentalism and valued ecumenical cooperation, particularly among liberal white Protestants, building alliances through groups such as the National Council of Churches (NCC). While the number of mainline Protestants has declined since the middle of the twentieth century, in the 1960s mainline Protestants constituted a prominent voice in public conversations. Their influence was so great that much of what historians tend to see as secular was actually deeply inflected with liberal Protestant values.