The Apocrypha are books of the Old Testament included in Roman Catholic and Orthodox Bibles as deuterocanonical (added to the earlier canon), but excluded from the Hebrew Bible and from most Protestant Bibles. It is not certain why the term apocrypha (hidden things) was originally applied to them, but they were considered less authoritative than the other biblical books because of their relatively late origin (c. 300 B.C. - A.D. 100). Except for 2 Esdras, which was in Latin, they were part of the Septuagint. The other books placed after the Old Testament in the Revised Standard Version are the following: 1 and 2 Esdras, Tobit, Judith, Additions to the Book of Esther, Wisdom, Sirach (Ecclesiasticus), Baruch and the Letter (Epistle) of Jeremiah, Additions to Daniel (Prayer of Azariah, Song of the Three Hebrew Children, History of Susanna, Bel and the Dragon), the Prayer of Manasseh, and 1 and 2 Maccabees.

Roman Catholic Bibles also list 1 and 2 Esdras and the Prayer of Manasseh as apocryphal. The Greek Orthodox Bible omits 2 Esdras but adds 3 Maccabees and Psalm 151, with 4 Maccabees as an appendix. The Apocrypha are important sources for Jewish history and religious developments in the 1st and 2nd centuries B.C.