(See Hayes 51 and in the Index on J, E, P, and D.)
The three sections of the Hebrew Bible--Torah, Nevi'im, and Ketuvim--seem to represent three successive stages of collection and redaction (the work of editing). They all contain material from as early as 1,200 BCE which was probably passed down in an oral tradition (i.e. by word of mouth). This material has been reworked and new material added during the period of collection. Although scholarship concerning the texts is by no means in clear agreement one popular theory has identified four sources from four periods of collecting, editing, and writing.
The earliest is the Yahwistic source (J), so called because it uses the JHWH title for the God of the Hebrews and also because these writings focus mainly on the southern part of the kingdom, known as Judah. The activity of collection of J dates from perhaps 1020-922 BCE, which is the period of the united kingdom of Israel.
Next comes the Elohistic source (E), so called because it uses the term Elohim for God and is particularly associated with the northern tribes of which Ephraim was the most important. This dates from approximately 922-722 BCE. That is to say from the division of Israel into the two kingdoms of Israel and Judah to the destruction of Israel by the Assyrians.
Then comes the Deuteronomic source of writings (D) which were collected between the fall of Israel to the Assyrians and the exile in Babylon (722-587 BCE). This is found mainly in the book of Deuteronomy and contains many legal stipulation used in the religious reforms made in 7th century BC Jerusalem.
The next period is the Priestly period (P) of the rigid canonization of the Torah after the first destruction of the Temple and during the exile in Babylon (587-520 BCE).
After this time no essentially new material was added to the Torah although editing and organizing the old material continued. In all probability the Torah was finalized and closed some time between the Exile and the rebuilding of the Temple in 520 BCE. The Nevi'im were completed before the Seleucid conquest of Palestine (c.200 BCE), and the Ketuvim between that date and the Maccabean revolt in 164 BCE.