The writ of habeas corpus primarily acts as a writ of inquiry, issued to test the reasons or grounds for restraint and detention. The writ of habeas corpus, also known as the Great Writ, is a U.S. legal process that determines whether an offender's imprisonment is valid.Habeas corpus is a Latin phrase meaning "produce the body. This Chapter explains an important right—the writ of habeas corpus. Federal habeas corpus is a procedure under which a federal court may review the legality of an individual's incarceration. Habeas corpus is essentially a safeguard against unjust incarceration. The "Great Writ" of habeas corpus is a fundamental right in the Constitution that protects against unlawful and indefinite imprisonment. (b) must state the reason why the detained person is unable to make the witness statement or affidavit. A Writ of Habeas Corpus is a civil proceeding that is available in both State and Federal Court to challenge the legality of imprisonment. In this lesson, students will explore the history and purpose of the Habeas Corpus clause in the Constitution.