Why does the Catholic Bible have 73 books and the Protestant 66?

Direct answer: the New Testament is the same in both Bibles — twenty-seven books, with no dispute. The entire difference lies in the Old Testament, where the Roman Catholic canon contains forty-six books and the Protestant canon thirty-nine, giving totals of seventy-three and sixty-six. The seven additional books are Tobit, Judith, Wisdom, Sirach (also called Ecclesiasticus), Baruch, 1 Maccabees and 2 Maccabees, together with longer forms of Esther and Daniel. The disagreement is older than the Reformation, and the Eastern Orthodox and Oriental Orthodox churches receive a wider Old Testament still, so the familiar "73 versus 66" is only two points on a longer line.

Which books are the disputed ones?

The Catechism of the Catholic Church states the count directly: forty-six books for the Old Testament — forty-five if Jeremiah and Lamentations are counted as one — and twenty-seven for the New.

Why do two canons exist at all?

Because there were two forms of the Hebrew Scriptures in circulation when Christianity began.

The Septuagint was a Greek translation of the Hebrew Scriptures made from roughly the third century BC onward for Greek-speaking Jewish communities, chiefly in Alexandria. It circulated with a broader set of writings than the collection that Jewish tradition later fixed. The early church, which spoke and wrote Greek, generally used the Septuagint; most Old Testament quotations in the New Testament follow its wording.

The Hebrew canon as later fixed by Jewish tradition contains the twenty-four books that correspond to the thirty-nine of the Protestant Old Testament, counted differently — Samuel, Kings and Chronicles each as one book, the twelve minor prophets as one, and Ezra-Nehemiah as one. Luke 24 reflects the threefold shape it was given: "the law of Moses, the prophets, and the psalms".

Christianity inherited both an origin in Judaism and a Greek Bible, and the tension between them is the whole story.

Was this settled before the Reformation?

Not fully, and the fourth century is where the disagreement is clearest. Jerome, translating the Bible into Latin, learned Hebrew and came to regard the books absent from the Hebrew collection as useful for edification but distinct in status; his prefaces say so. Augustine, his contemporary, treated them as Scripture, and the North African councils of the 390s listed them.

Jerome translated them anyway. The Vulgate carried them, and Western Christendom read them as Scripture for a thousand years, with the older reservation preserved in the manuscripts and available to anyone who read the prefaces.

What happened at the Reformation?

Martin Luther, translating the Bible into German, followed Jerome's line rather than Augustine's: he grouped the disputed books together in a separate section between the Testaments, with a heading indicating that they were useful and good to read but not equal to Holy Scripture. Other Reformation Bibles did the same, and the King James Version of 1611 likewise printed the Apocrypha as a separate section between the Testaments — a practice that continued in English Bibles for over two centuries before printing costs and Bible-society policy removed it from most editions.

The Council of Trent, in 1546, responded by defining the canon of forty-six Old Testament books for the Roman Catholic Church. The Protestant confessions of the following century did the reverse, restricting the Old Testament to the Hebrew collection.

So the two canons were formalized in the sixteenth century, but neither side invented its position then. Both were choosing between options that had been present since the fourth.

What do the Orthodox churches receive?

More than either, and not uniformly. The Eastern Orthodox churches generally receive the Septuagint Old Testament, which includes the seven books above and also 1 Esdras, 3 Maccabees, the Prayer of Manasseh and Psalm 151, with 4 Maccabees often printed as an appendix. The Oriental Orthodox churches vary, and the Ethiopian Orthodox Tewahedo Church has the broadest canon in Christianity, receiving works including 1 Enoch and Jubilees that no other tradition treats as Scripture.

Anyone quoting a single number for "the Orthodox Bible" is simplifying a genuine variation.

Does the difference change Christian doctrine?

It matters at specific points rather than everywhere. 2 Maccabees 12 contains the passage most cited in support of prayer for the dead, which is one reason the canon question and the purgatory question have travelled together since the sixteenth century. Wisdom and Sirach are quoted extensively in Catholic and Orthodox liturgy. The books also fill in the historical gap between the Old and New Testaments — the Maccabean revolt is where the festival of Hanukkah, mentioned in John 10:22 as the Feast of the Dedication, comes from.

What the difference does not do is create two different Gospels. The New Testament is identical, and the doctrinal core that the historic creeds state is drawn from books that every tradition receives.

Do the New Testament writers quote these books?

They allude to them, and the picture is more interesting than either side's summary.

Hebrews 11:35 appears to allude to the martyrdoms narrated in 2 Maccabees 7. The letter of James has repeated verbal contacts with Sirach. And John 10 places Jesus in Jerusalem at "the Feast of the Dedication" — Hanukkah, a festival whose origin is narrated in 1 Maccabees, a book Protestants do not receive as Scripture.

The complication cuts the other way too. Jude quotes a book that no Western tradition receives at all:

About these also Enoch, the seventh from Adam, prophesied, saying, “Behold, the Lord came with ten thousands of his holy ones, to execute judgment on all…” (Jude 14-15)

That is 1 Enoch, canonical only for the Ethiopian Orthodox Tewahedo Church. So quotation by a New Testament writer is not, by itself, the test either side uses — which is precisely why the argument has never been settled by counting citations.

Terms worth keeping straight

• Deuterocanonical means "of the second canon" — received into the canon at a second stage. It is the Catholic and Orthodox term and is not a synonym for doubtful.
• Apocrypha means "hidden" and is the Protestant term for the same books. Confusingly, it is also used for a quite different set of writings — the New Testament apocrypha, such as the Gospel of Thomas — which no Christian tradition receives as Scripture.
• Pseudepigrapha covers works attributed to ancient figures who did not write them, including 1 Enoch and Jubilees.

Which set of books your own Bible contains is worth checking on the contents page rather than assuming; the differences between editions are described in how to start reading the Bible, and the translation published here is documented on the translations and licenses page.

Bible text: World English Bible (public domain). This article describes what the text says and what different Christian traditions teach; it does not recommend one of them.