What does it mean to condition federal tax liability on the degree to which a Native American has assimilated? Native Americans have been long presumed to be subject to federal income taxation despite the absence of express congressional authorization. This presumption obscures the complicated history by which Native Americans were incorporated into the federal tax base. This Article provides a normative, long-overdue description of Native federal income tax liability by situating that historical path within the longer trajectory of federal Indian law. This Article traces how an assimilative framework that includes allotment policy, competence determinations, and the Indian Citizenship Act of 1924 collectively transformed Tribal members from “Indians not taxed” into presumed taxpayers. Historical federal taxation jurisprudence required that Native Americans abandon their Tribal membership to be taxable. But now, courts quietly ignore this requirement. The failure to resolve the impact of dual citizenship—the coexistence of U.S. citizenship with continued Tribal citizenship—collapses political distinctness into presumptive assimilation. By excavating this history, this Article demonstrates that Native federal income taxation is neither inevitable nor doctrinally coherent. It argues that courts have misapplied statutory canons of interpretation by privileging the presumption of taxability over Indian canons of construction, which require express congressional intent for courts to impose a statute of general applicability on Tribal citizens. But more fundamentally, this Article contends that taxation doctrine has failed to account for the implications of Native dual citizenship, thereby erasing the sovereign-to-sovereign relationship that the law otherwise recognizes.