The writ of habeas corpus has been described by the Supreme Court as “a bulwark against convictions that violate fundamental fairness” and as “the judicial method of lifting undue restraints upon personal liberty.” At common law, however, the writ of habeas corpus was available only before conviction and only for the purpose of establishing that sufficient legal cause existed for a prisoner’s detention. It was for a court of competent jurisdiction to determine guilt or innocence, and habeas corpus was not intended to disturb that determination. Instead, the appellate process was the exclusive remedy for legal errors and the writ of habeas corpus served the more limited role of protecting citizens against detention by the arbitrary will of a public official without sufficient legal cause. Over time, however, the Court became more concerned with fundamental fairness and ensuring that innocent individuals were not being incarcerated. Habeas corpus became one tool in the Court’s arsenal to combat such abuses. Providing defendants with an opportunity to relitigate federal claims in federal courts was thought to protect against potential state court bias and ensure that those in prison were actually guilty of the offenses for which they had been incarcerated. Balanced against the desire to ensure fairness, however, were the Court’s concerns about federalism, finality, and conservation of judicial resources. Consequently, for each expansion of the writ’s scope to increase fairness to defendants, there was a concomitant contraction elsewhere to promote interests in finality, federalism, and conservation of resources. This course will consider the purpose of the Great Writ, explore its historical development, and examine the ways in which the courts and legislatures have expanded and contracted the writ over time.