The Fourteenth Amendment enshrines a commitment to birthright citizenship that extends to almost anyone born in the United States. While the federal government is the arbiter of questions of citizenship, the states are indispensable partners: State-issued birth certificates have long been the preeminent form of proof of birthright citizenship. However, federal agencies’ treatment of delayed birth certificates—which are usually held by individuals marginalized by race, class, and geography—depart from the usual federal acceptance of states’ determinations of birth facts. Delayed birth certificates, including those issued pursuant to state court orders grounded in judicial factfinding, may be rejected by federal agencies like the Department of State and Social Security Administration as proof of U.S. citizenship. In exploring the relationship between federal agencies and state institutions with respect to the recognition of birthright citizenship, this Article highlights both the human consequences of the current arrangement, as well as the inability of existing scholarship on cooperative federalism and immigration federalism to account for this unique manifestation of federal-state collaboration. It argues that when federal and state governments reach different conclusions about a person’ s entitlement to birthright citizenship, they create an untenable conflict between sovereigns that leaves unknown numbers of de jure U.S. citizens experiencing the de facto denial of citizenship. The Article concludes with recommendations for mitigating this conflicting state of affairs.