The idea of religious liberty is so normative to the modern world that it is enshrined in The United Nations' Universal Declaration of Human Rights. Despite its significance, however, its history is not well understood; there is a popular myth that religious liberty was a secular invention of the eighteenth-century European Enlightenment. The annual Richard Johnson Lecture 2020 sets out to debunk this myth by unearthing something of the forgotten history of religious liberty. I chart the evolution of the concept of religious liberty and the intertwined ideas of freedom of conscience and the free exercise of religion. This intellectual history focuses on five seminal historical moments: the origins of the New Testament idea of conscience in the first-century Mediterranean world; the development of conscience as a right in medieval natural law; the toleration of religious minorities and arguments for freedom of conscience amidst the bloodshed of the Protestant Reformation; the codification of the idea of religious liberty at law in various states in the eighteenth-century Atlantic world; and the negotiation of this tradition of religious liberty in colonial Australia. This intellectual history enriches our historical understanding of one of the most poignant and contested religious ideas in the contemporary world.In 1943, a German Lutheran pastor was arrested. He had refused to take an oath of loyalty to the then leader of Germany, believing that a Christian could only swear such complete loyalty to Jesus. Out of his Christian convictions, he took part in operations to help German Jews escape the Holocaust to Switzerland and to oppose Adolf Hitler. In a country that no longer protected the freedom of religion and in fact where the state attempted to control the church, the state was able to silence dissenting voices.At dawn on the 9 April 1945, Dietrich Bonhoeffer was brought out of his cell at Flossenburg concentration camp. He was stripped of his clothes and led naked to the gallows where he was hangedtwo weeks before the