Part I explores recent aspects of the detention debate: the procedural novelty of the Federal Bail Reform Act of 1984 and the analytic novelty of United States v. Salerno (1987), in which the U.S. Supreme Court relied on the use of detention without trial at a variety of points throughout the criminal justice, civil justice, and mental health systems including the juvenile detention case of Schall v. Martin (1984). Part I argues that the essential notion of punishment is overlooked in the detention debate, and it considers the need for a constitutional conception of punishment to replace the U.S. Supreme Court's assertion that detention on the basis of predicted criminality is not punishment. Part I then considers the theoretical and practical problems with the latest magic formula in the detention debate, i.e., the use of predictions of future dangerousness to determine who should be detained prior to trial. Part II departs from current issues and identifies a series of trade-offs that any criminal justice system must make in setting rules for detention. Part II identifies essential decisions that distinguish one detention system from another and explores the current practices in the United States within this framework. This article offers a theory of detention that accommodates fundamental constitutional and jurisprudential principles, the traditional grounds for detention, and the notion that the State should detain high-risk offenders whom it arrests for serious offenses during a period of pretrial release. 468 footnotes