On Christian Doctrine is a theological text written by St. Augustine of Hippo. It consists of four books that describe how to interpret and teach the Scriptures. The first three of these books were published in 397 and the fourth added in 426. By writing this text, St. Augustine set three tasks for Christian teachers and preachers: to discover the truth in the contents of the Scriptures, to teach the truth from the Scriptures, and to defend scriptural truth when it was attacked.