Jewish tradition has counted The Twelve as a single book since antiquity, a practice already reflected in the deuterocanonical Book of Sirach around 180 BCE, which refers to "the bones of the twelve prophets" as a known, unified collection, and this counting affects the Hebrew Bible's traditional total of twenty four books, which becomes thirty nine in Christian Old Testaments largely through splitting Samuel, Kings, Chronicles, Ezra-Nehemiah and The Twelve into smaller units.
Scholars have increasingly studied The Twelve as a deliberately shaped anthology rather than a mere anthology of convenience, noting shared catchwords and themes that bridge adjoining books and a rough overall movement from judgment in the earlier prophets to restoration in the later ones, evidence of real editorial intention in how the twelve were selected, ordered and joined. Individual books within the collection carry their own well documented critical questions distinct from the collection as a whole: Jonah's highly stylized, almost fable-like narrative structure and its concern with a much later question, whether God's mercy extends to Israel's enemies, leads most critical scholars to read it as a later didactic composition using an earlier prophet's name rather than a first person prophetic memoir, while roughly half of Zechariah, chapters 9 through 14, differs enough in style and historical horizon from chapters 1 through 8 that many scholars attribute it to a later, anonymous continuation.