Modern debates about the limits imposed by the Suspension Clause on the Executive’s power to detain citizens without criminal charges during wartime have largely taken place without historical reference to what the Founding generation understood the “Privilege of the Writ of Habeas Corpus” to mean. These debates likewise have largely failed to account for how the Founding generation viewed the relationship between the privilege and the provision for its suspension included in the Suspension Clause. Meanwhile, the Supreme Court has emphasized that the Suspension Clause analysis should be guided at a minimum by an understanding of the legal status of the privilege at the time of ratification. This Article seeks to fill this void by exploring the historical record to provide an account of what the Founding generation understood the constitutional “Privilege of the Writ of Habeas Corpus” to be. The evidence explored herein reveals that by the Founding period, the privilege had come to encompass a general right of persons owing allegiance and thereby enjoying the protection of domestic law – most especially citizens – not to be detained without charges for criminal or national security purposes in the absence of a valid suspension. This conclusion follows from the strong connection forged in the period leading up to ratification between the privilege and a host of individual rights – including the rights to presentment or indictment, reasonable bail, and speedy trial – many of which were promised by the Habeas Corpus Act of 1679. As this Article also explores, throughout the Founding period and well through Reconstruction, it was virtually taken for granted that where a valid suspension was not in place – even during wartime – citizens owing allegiance who were suspected of supporting the enemy could only be detained on American soil pursuant to substantiated criminal charges. Consistent with this principle, the history reveals that the entire point of suspending the privilege was to endow the Executive with the power to arrest and detain such persons without criminal charges in times of war. The Article concludes by discussing how this history calls into question the constitutionality of the internment of Japanese Americans during World War II and the detention of American citizens as so-called “enemy combatants” in the wake of the attacks of September 11, 2001.