Abstract: In the course of vindicating the right to habeas corpus for military prisoners at Guantanamo Bay Naval Base, the Supreme Court had occasion to resolve a series of previously open questions about the meaning of the Constitution's Habeas Corpus Suspension Clause. In this Essay, Professor Neuman examines the implications of the Court's interpretation for habeas corpus law more generally, in civil and criminal contexts within the United States. The Suspension Clause guarantees a permanent minimum content for the judicial remedy against unlawful detention of either citizens or aliens. The constitutionally necessary scope of review is determined partly by historical inquiry, and partly by an instrumental balancing test. Stricter standards apply to review of executive detention, but the Clause may also require some check on judicially ordered detention. The Court's analysis further suggests that the Suspension Clause is best understood today as affirmatively mandating a federal remedy, and not merely as protecting state remedies from federal interference. This Essay explores the consequences of this account for recent controversies over judicial power to provide effective review of decisions removing aliens from the United States, and thereby illustrates the uncertain operation of the Court's new balancing approach.