The four-source theory

Originally, many thought Moses wrote all the Torah, the first five books of the Bible.  Bible scholars of the last century have been able to locate four distinct strands, the Jahwist (J) the oldest from around 950 BCE, the Elohist (E) from around 850 BCE, the Deuteronomist (D) from around 650 BCE, and the later Priestly (P) sources around 600-400 BCE.  The Priestly source put it altogether after the exile around 450 BCE, long after the death of Moses.  Some scholars have developed more elaborate documentary hypothesis within this source theory.