Michael D. Coogan, The Old Testament: A Historical and Literary Introduction to the Hebrew Scriptures, third edition (Oxford University Press, 2014), 10-11.
Although some ancient and most modern authors have produced single works that remain essentially unchanged, that was not the case with many books of the Bible. They often went through several editions over the course of several centuries – editions that sometimes included major revisions, expansions, and rearrangement. The book of Jeremiah tells us that the prophet originally dictated his prophecies or “oracles” to his scribe Baruch, who wrote them down (Jer 36:1-4, 32). So in theory, at least, there was an original. But that original was expanded by stories about the prophet, told in the third person, and therefore not by the prophet himself, and by much other material; these expansions may have taken place in different ways at different times and places. When we compare manuscripts of the book of Jeremiah, whatever its original may have been, we find very different versions. The traditional Hebrew Masoretic Text is roughly 15 percent longer than that found in the Septuagint and in some manuscripts among the Dead Sea Scrolls, and the order of some of the chapters also differs. Similar editorial processes are evident in many other books of the Old Testament, and the study of these processes is called redaction criticism.