From Bible Encyclopedia
The Old Testament Hebrew Scriptures are the collection of books that forms the first of the two-part Christian Biblical canon. The contents of the Old Testament canon vary from church to church, with the Orthodox communion having 51 books: the shared books are those of the shortest canon, that of the major Protestant communions, with 39 books.
All Old Testament canons are related to the Jewish Bible Canon (Tanakh), but with variations. The most important of these variations is a change to the order of the books: the Hebrew Bible ends with the Book of Chronicles, which describes Israel restored to the Promised Land and the Temple restored in Jerusalem; in the Hebrew Bible God's purpose is thus fulfilled and the divine history is at an end, according to Dispensationalism and Supersessionism (see Jewish Eschatology for Jewish beliefs on the subject). In the Christian Old Testament the Book of Malachi is placed last, so that a prophecy of the coming of the Messiah leads into the birth of the Christ in the Gospel of Matthew.