The Apology of the Augsburg Confession was prepared by Philipp Melanchthon as a response to the Roman Catholic "Confutation of the Augsburg Confession" which was written to answer the Lutheran Augsburg Confession after it was presented in 1530 at the Diet of Augsburg. Melanchthon wrote this as a defense of the original Confession, and a refutation of this Confutation that Emperor Charles V had commissioned. The Book of Concord includes it as a Lutheran confessional document. It is the longest document in the Book of Concord and offers the most detailed Lutheran response to the Roman Catholicism, as well as the most detailed Lutheran explanation of the doctrine of justification.