At first glance, Catholic and Protestant Bibles look the same, with the same basic books collected together in a single volume. However, at closer look, a Protestant Bible is missing several books that are included in a Catholic Bible.
Why is that?
First off, Christians did not have a single volume of inspired texts for roughly the first 300 years. The creation and compilation of the Bible was a long process. Leaders of the early Church sifted through numerous manuscripts and discerned, using several different historical, doctrinal, and theological criteria, which books were to be kept and included in the canon, and which books were to be set aside.
The Old Testament was largely based on a Greek translation of the Hebrew texts that became widely accepted as a legitimate (and even inspired) translation. This is known as the "Septuagint" (from the Greek word for 70) and was especially popular among Greek-speaking Jews.
The approval of which books to include in the New Testament started with the Council of Laodicea in 363, was continued when Pope Damasus I commissioned St. Jerome to translate the Scriptures into Latin in 382, and was settled definitely during the Synods of Hippo (393) and Carthage (397).
The goal was to dismiss all erroneous works that were circulating at the time and instruct the local Churches as to which books could be read at Mass.
As a result of these synods, the Bible remained unchanged until the Protestant reformation.
After the 16th century, each major Protestant leader had different interpretations regarding the Christian faith and the role of the Bible. This led to a process where various books of the Bible were removed on account of their "incompatibility" with Protestant beliefs.
Furthermore, Protestants typically use a list of books of the Old Testament that were approved by Hebrew scholars at a later date, possibly by the 2nd or 3rd century AD. Catholics, on the other hand, use the Greek Septuagint as the primary basis for the Old Testament.
This means that Protestant Bibles have only 39 books in the Old Testament, while Catholic Bibles have 46. The seven additional books included in Catholic Bibles are Tobit, Judith, 1 and 2 Maccabees, Wisdom, Sirach, and Baruch. The Catholic canon also includes sections of the Books of Esther and Daniel that are not found in Protestant Bibles.
Some Protestant bibles still include these books, while others do not. Since there are many Protestant denominations throughout the world, the list varies according to the practices of each Christian church.