Abstract: This article explores the debates over slavery and abolitionism within the American Board of Commissioners for Foreign Missions (ABCFM). While historians have explored many aspects of the ways that abolitionism presented a crisis that would tear white American Protestantism apart, the ABCFM debates draws our attention to two key subjects: the ongoing work of defining the boundaries between religion and politics, and the moral implications of the choices that missionaries made as they developed new arguments about those boundaries in the 1840s and 1850s. As abolitionist critics demanded that the ABCFM take a stance against slavery, the missionary organization insisted that it could not do so because slavery was a political, and not a religious, question. The resulting debates covered not only the topics of slavery and abolition, but those of the nature of sin, Christianity, and missionary work itself. The ABCFM’s insistence that the question of slavery was political , not religious , reveals the ways that organizations like the ABCFM deployed the management of the definition of religion selectively and provides new insights into both the effect of abolitionism on American Protestantism and the ongoing tension between Christ and culture in the mission field.