Conventional wisdom maintains that the Supreme Court banished general law from federal courts in 1938 in Erie Railroad Co. v. Tompkins when the Court overruled Swift v. Tyson. The narrative asserts that Swift viewed the common law as a “brooding omnipresence,” and authorized federal courts to disregard state common law in favor of general common law of their own choosing. The narrative continues that Erie constrained such judicial lawmaking by banishing general law from federal courts. Contrary to this account, Swift and Erie represent compatible conceptions of federal judicial power when each decision is understood in historical context. At the time Swift was decided, federal courts applied general commercial law only in circumstances in which states applied general commercial law. The ensuing “Swift doctrine” ran into constitutional difficulties over time because states gradually abandoned general commercial law in favor of local state law, while federal courts steadily expanded the application of general law beyond its traditional bounds. In Erie, the Supreme Court rejected the federal courts’ practice of applying general law in lieu of state law when they had no basis in the Constitution or an act of Congress for doing so. But Erie did not banish general law from federal court under all circumstances. Under Erie, federal judicial application of general law is problematic only when it disregards governing state law with no basis in the Supremacy Clause for doing so. Erie does not prohibit federal courts from applying principles derived from general law when necessary to uphold or implement basic features of the constitutional structure that lie beyond the regulatory authority of the states.