Diognetus, Letter To (Διόγνητος, Diognētos). A brief apologetic treatise written in Greek in the late second century to the pagan Diognetus. While never included in a canon list, this letter was accepted as authentic in the early church, and is part of a collection known as the Apostolic Fathers. The author and date of this articulate exposition of Christianity is a mystery. The only source available for Letter of Diognetus was a single medieval manuscript, but it was destroyed by fire in the 19th century; today, reconstructions are based upon transcriptions which disagree at times. The Letter of Diognetus provides moral comment on the foolishness of idolatry and on Christian character and behavior in the world.

(For more information on the Apostolic Fathers, see this article: Apostolic Fathers. For information on the process of canonization, see this article: Canon, New Testament.)