The Old Testament constitutes the first major part of the Christian Bible. It contains about 39 books, beginning with the book of Genesis. The exact number depends on how they are divided and whether certain disputed books are included; see Deuterocanon. They are usually divided into the categories law, history, poetry and prophecy. All of those books were written before the birth of Christ.
Loosely speaking, the Christian Old Testament corresponds to the Jewish Scriptures (Tanach) , except that both versions have a a slightly different order (of books). The Christians call this group of books the Old Testament, because of a belief (taught in the Epistle to the Hebrews) that there is a new covenant or testament between God and mankind, after the coming of Jesus. Jews themselves do not accept the New Testament or the characterization of the Tanach as the Old Testament (although many Jews accept Jesus as a historical figure and pious Jew). There is some debate among christian scholars over the issue of whether the New Testament applies to Jewish people, but there is very little debate over its applicability to Gentiles. Similarly, the degree to which the Old Testament and its laws applies to christians is a debated point.
The New Testament text however does contain many references to the Old Testament, especially in relation to the fulfillment of prophecies concerning the promised messiah, whom Christians believe to be Jesus Christ. In Christian theological view this expectation, present fulfillment and eschatological fulfillment of the divine, eternal kingdom under the headship of Christ are the read thread running through both Testaments.