Basement faults in the southern Appalachian–Ouachita footwall and foreland include crustal-scale rift and transform elements of the late Proterozoic–Cambrian Iapetan rifted margin of southern Laurentia, synrift intracratonic basement fault systems in rift-parallel and transform-parallel orientations, and down-to-basin basement faults in late Paleozoic foreland basins. Late Paleozoic emplacement of allochthons accommodated a sinuous trace, mimicking the embayments and promontories of the Iapetan continental margin. Late Paleozoic tectonic loading reactivated synrift intracratonic faults, and either reactivated or initiated down-to-basin fault systems in foreland basins. Basement faults in the orogenic footwall localized thin-skinned thrust ramps, demonstrating interplay of causes and effects in the interactions between basement faults and the southern Appalachian–Ouachita orogen.