Important recent scholarship shows that the Habeas Corpus Suspension Clause is aimed mainly at substantive legislation that authorizes confinement by the executive that otherwise would be unlawful. Thus a grant of detention authority that leaves the judicial habeas corpus remedy intact can constitute a suspension subject to the clause. This article emphasizes that at the time of the framing the central example of a suspension of the writ was a grant of extremely broad discretion to the executive to confine people the executive believed to be dangerous. It maintains that broad executive discretion to confine is a necessary condition for a grant of detention authority to qualify as a suspension. Therefore legislative authorization of executive detention for reasons of national security is not a suspension as long as the executive’s discretion is substantially bounded; for example, the confinement of enemy aliens during war does not require suspension of the writ. That is true whether the persons to be detained are citizens or aliens. Congressional grants of legally determinate national security detention authority are thus not limited to cases of rebellion and invasion by the Suspension Clause, because they are not suspensions, and may be applied to citizens and aliens alike.