Abstract: Judges must often decide what law governs issues in their cases - state law or federal common law. Scholars have traditionally divided this inquiry into two stages, asking first whether the judge has power to apply any law other than state law, and then, if such power exists, whether the judge should apply state law anyway. In this Article, Professor Field challenges this two-prong inquiry and the conception of "state law" that it implies. She argues that the power to create federal common law is (and should be) much broader than is generally assumed, and that despite Erie Railroad v. Tompkins, state law very rarely "operates of its own force." Professor Field concludes that even though there is broad power to create federal common law, judges have exercised their discretion in a way that allows state law and federal common law to operate in a complementary fashion.