The idea of conscience has its origin in the 5th Century BCE as awareness of a shameful or guilty secret. Soon the idea expanded to include awareness of avoidable future wrongdoing. St. Paul thought the awareness fallible, even though it drew from a divine law written in our hearts. Even today, the concept retains its value. In this lecture, Richard Sorabij will focus on the early history and modern transformations of the concept, including the freedom of conscience and the penitent’s conscience.