First, the superscription functions as a heading not only for chapters 1–12 or 1–39 but for the entire book of Isaiah. Second, although the book is called a prophetic “vision,” only a few parts of it fit the term. In other words, the superscription expresses a certain— and presumably late—understanding of the prophetic mission; the entire book is considered a divine revelation. Third, every reader knows that the Judean kings listed in 1:1 belong to the eighth century and the lifetime of the prophet Isaiah but do not cover the second part of the book, chapters 40–66. The mention of Cyrus, king of Persia (Isa 44:28; 45:1) suggests another historical background. These basic observations led rather early to the thesis of multiple authorship: chapters 1–39 (Proto-Isaiah) contain the words of the prophet Isaiah from the eighth century; chapters 40–55 are traced back to an anonymous writer in the Babylonian exile called Deutero-Isaiah; and the third part of the book, Isa 56–66 (Trito-Isaiah), is attributed to a post-exilic prophet also unknown to us.

The three-part division of the book of Isaiah into Proto-, Deutero-, and Trito-Isaiah is usually associated with Bernhard Duhm (1847–1928) and his epoch-making commentary on Isaiah (1892) (Duhm, Buch Jesaia, v–xix). But long before Duhm, it was widely understood that from Isa 40 onward, an author other than the one of the first thirty-nine chapters of the book was speaking (Moser, Umstrittene Prophetie). In his notes he also commented briefly on some parts of the book of Isaiah that, in Koppe’s view, could not longer be attributed to the eighth-century prophet. These included not just the oracle against Moab in Isa 15–16 and Isa 30:1–27, but also chapter 50, which he dated to the time of the exile (Cf. Lowth, Jesaias, vol. 2 (1780), 43, 130, 233–234 (see Moser, Umstrittene Prophetie, 11–13)).

Duhm’s achievement essentially consisted in the further elucidation of this concept. Both the differentiation between Deutero-Isaiah and Trito-Isaiah and the disentanglement of the Servant Songs of Isa 42:1–4; 49:1–6; 50:4–9; and 52:13–53:12 came to be associated with his name. Furthermore, he demonstrated in his commentary that considerable portions of Proto-Isaiah could not be traced back to the prophet of the eighth century but were to be dated in part to a much later time (Cf. Duhm, Jesaja, 18–22). Duhm considered, for example, that the Isaiah legends of Isa 36–39 might have originated in the time of Ezra. He dated Isa 23:1–14 and 19:1–15 to the fourth century and went so far as to date the socalled Isaiah Apocalypse (Isa 24–27) in the second century. So Duhm assumed a comprehensive history of development for the first part of the book of Isaiah, which spanned the eighth century to the second century bce. Strangely enough, Duhm did not pursue the idea that the growth of Proto-Isaiah could have also encompassed the origins of Deutero-Isaiah and Trito-Isaiah.

Three major phases in the history of composition of Isa 56–66 can be delineated:

• 1. In the first stage, Isa 40–55 was expanded by the basic components of Isa 60–62. Its themes are the glorification of Zion, the return of the diaspora, and the role of the nations. Later segments within Isa 60–62 (e.g., 62:10–12) already presuppose ProtoIsaiah (cf. Isa 35).
• 2. A further expansion in Isa 56–59, once again composed of various clusters, is concerned with the conditions of salvation, which has evidently not proceeded as expected in Isa 60–62. The reason for the delay in salvation is found in the deplorable state of affairs in Jerusalem, which may only be alleviated through repentance. A division among the people of God is thus indicated.
• 3. The last great stage encompasses the (not itself unified) complex of Isa 63–66. A great lament of the servants of God is found in Isa 63:7–64:11 (an expansionary segment composed for this context). There is, in addition, a response to the lament in Isa 65–66, which announces the demise of those who abandon Yhwh and attach themselves to the worship of idols. At the same time, these chapters lead back to the beginning of the book, in Isa 1. In the final phases of the book of Isaiah, a division among the people of God is already taken for granted.