composed during the Babylonian captivity and later. The consensus through most of the 20th century, that the book comprises three separate collections of oracles: Proto-Isaiah (chapters 1-39), containing the words of Isaiah; Deutero-Isaiah (chapters 40-55), the work of an anonymous 6th-century BCE author writing during the Exile; and Trito-Isaiah (chapters 56-66), composed after the return from Exile. While virtually no scholars today attribute the entire book, or even most of it, to one person, the book's essential unity has become a focus in current research.