This study traces the transition of treason from a personal crime against a monarch to a more modern crime against the impersonal state. Prior to the Civil Wars of the 1640s, English jurists construed the law of treason largely as a personal crime against the monarch. The book reveals how the events of the 1640s challenged pre-existing interpretations and led to a revised understanding of treason as a crime committed against "the state" as an impersonal entity.