Abstract: After more than 200 years, the Full Faith and Credit Clause remains poorly understood. The Clause first issues a self-executing command (that “Full Faith and Credit shall be given”), and then gives Congress power to prescribe the manner of proof and the “Effect” of state records in other states. But if states must accord each other full faith and credit—and if nothing could be more than full—then what “Effect” could Congress give state records that they wouldn’t have already? And conversely, how could Congress in any way reduce or alter the faith and credit that is due? This Article seeks to answer these questions in light of Congress’s early efforts, from the Founding to the 1820s, to “declare the Effect” of state records—efforts which have largely escaped the notice of current scholarship on the Clause. Together with pre-Founding documents and the decisions of influential state courts, they suggest that the Clause was not generally understood to mandate the effect of state records in other states, but rather to leave such determinations to the legislative branch. Indeed, early interpreters of the Clause attributed far less importance to its first self-executing sentence, which was often understood as a rule of evidence, and far more importance to the Congressional power to determine substantive effect. Recovering this original meaning not only saves the Clause from obscurity, but also offers opportunities for deliberation and legislative choice over the structure of our federal system.