Protestants and Roman Catholics share the whole of the New Testament and 39 books of the Old Testament, though Esther and Daniel have a few additions in the Roman Catholic Bible, and their Bible includes 6 extra books
and First and Second Maccabees
The Catholic Encyclopedia says that they have 45 books in the Old Testament and 27 in the New, making a total of 72 books.
Protestants will tell you that we have 66 books in our Bibles: the same 27 in our New Testaments and 39 in our Old Testament.
But several of these books should really be grouped together. Exodus-Numbers is really one continuous narrative, Samuel-Kings is really one book [and divided in illogical places in our Bibles], Chronicles is also one book, as are Ezra and Nehemiah. So our Old Testament is really a collection of 31 books. The Books of the Bible: a presentation of Today's New International Version also joins Chronicles with Ezra-Nehemiah, but this is not done in the Tenach [the Jewish Old Testament].
There is also one modification to make in the New Testament, because Luke-Acts is really one work in two volumes, thus reducing the New Testament to 26 books, giving us a total of 57 books in a Protestant Bible.