Christianity is a Semitic religion, which claims to have nearly 1.2 billion adherents all over the world. Christianity owes its name to Jesus Christ (peace be on him). The Holy Bible is the sacred scripture of the Christians:
a) The Bible is divided into two parts, the Old Testament and the New Testament. The Old Testament is the Holy Scripture of the Jews and contains records of all the prophets of the Jews that came before Jesus (pbuh).
The New Testament contains records of the life of Jesus (pbuh).
b) The complete Bible, i.e. the Old Testament and the New Testament put together, contains 73 books. However, the Protestant Bible i.e. the King James Version, contains only 66 books as they consider 7 books of the Old Testament to be apocrypha, i.e. of doubtful authority.
Therefore the Old Testament of the Catholics, contains 46 books and that of the Protestants, 39 books. However the New Testament of both these sects contains 27 books.
(Reference: http://www.irf.net/irf/comparativereligion/index.htm )