"Presumptions," Orma Linford has pointed out, "are the balancing blocks in striking a balance between majority rule and minority rights, between liberty and order, between established social rules and religious freedom." Two interrelated presumptions underlay the nineteenth-century campaign against Mormon plural marriage that is reviewed in this essay. The first was that an institution so repugnant to conventional Christian values as polygamy could not qualify as an "exercise of religion" presumptively entitled to protection under the First Amendment. The second was that Mormon plural marriage, whatever its practitioners might believe or say about it, was "an overt act against peace and good order" (Jefferson's phrase) and therefore ineligible for constitutional protection. These presumptions, Linford notes, eventually paved the way "for any kind of action Congress desired to take." She might have included acts by several territorial and state legislatures and added that the same presumptions led the federal courts to sustain almost all such measures.