In this statement before the Senate Judiciary Committee, Mariano-Florentino Cuéllar addresses the relationship between habeas corpus, executive discretion, and national security--an issue that has occasioned much debate among legal scholars, lawyers, lawmakers, and the public in recent years. This issue has taken on particular urgency given the recent passage of the Military Commissions Act (MCA).1 Section 1005(e)(1) of this Act strips American courts of jurisdiction to consider habeas corpus applications involving aliens accused of being enemy combatants, effectively allowing any decisionmaker appointed by the President to detain an alien indefinitely by merely accusing her of being an enemy combatant. Cuéllar analyzes this provision in light of history, American legal traditions, and the institutional realities affecting the performance of executive bureaucracies.