The concept of habeas corpus-literally, to receive and hold the body-empowers courts to protect the right of prisoners to know the basis on which they are being held by the government and grant prisoners their freedom when they are held unlawfully. It is no wonder that habeas corpus has long been considered essential to freedom. This Very Short Introduction chronicles the storied writ of habeas corpus and how its common law and statutory origins spread from England throughout the British Empire and beyond, witnessing its use today around the world in nations as varied as Canada, Israel, India, and South Korea. Beginning with the English origins of the writ, the book traces its historical development both as a part of the common law and as a parliamentary creation born out of the English Habeas Corpus Act of 1679. The book then takes the story forward to explore how the writ has functioned in the centuries since, including its controversial suspension by President Abraham Lincoln during the Civil War. It also analyzes the major role habeas corpus has played in such issues as the World War II incarceration of Japanese Americans and the US Supreme Court's recognition during the War on Terror of the concept of a "citizen enemy combatant."