The origin of the word apocryphon is Greek, meaning "closed" or "hidden". This refers to the books being kept away from common souls. St. Jerome (Hieronymus, ca. 342-420) used the word to indicate the books that were not part of the Jewish Bible, the Tanakh, but were included in the Greek Septuagint Bible. Today the word usually refers to a series of mostly pre-Christian religious books not part of the official, canonical Bible.

Most of the apocryphal books in the King James Version are part of the Old Testament in the Catholic Bible. Catholics refer to these books as deuterocanonical: they are part of the Bible (i.e. canonical), but became so only after the first list had been determined (hence deutero). The deuterocanonical books of the Old Testament are: Tobit, Judith, Wisdom of Solomon, Sirach, Baruch, 1 en 2 Maccabees and the Additions to Daniel and Esther. Some books in the New Testament are also considered deuterocanonical: Hebrews, 2 Peter, 2 and 3 John, James, Jude and Revelation. Protestants, however, regard these books as fully canonical.

In the original 1611 edition of the King James Version the Apocrypha were inserted between the Old and the New Testament. In later editions they were often omitted, partly for economical reasons, partly because they were considered increasingly less important.

The texts were mostly written in the 2nd and 1st centuries BC, most of them in Greek. Some were probably originally in Hebrew, but because from the 1st century AD onwards Jewish scholars did not consider them part of the Tanakh, the original copies were lost. One Hebrew copy of Sirach has survived.

Apocrypha included in the King James Version: