Recent research on the book of Isaiah has been dominated by discussions of its unity and authorship. Professor Williamson's important study provides a major and highly original contribution to these key issues, and is based upon a more rigorous methodology than ever used before. Isaiah is usually regarded as the work of two authors - the so-called Isaiah of Jerusalem (Isaiah 1-39) and Deutero-Isaiah (the author of Isaiah 40-55). Professor Williamson argues that the author of Isaiah 40-55 was in fact strongly influenced by the work of the earlier writer. Secondly, he demonstrates that the earlier work was regarded as a book which had been sealed up until the time when judgement was past and the day of salvation had arrived, and that Deutero-Isaiah believed himself to be heralding the arrival of that day. Thirdly, and most provocatively, Professor Williamson argues that Deutero-Isaiah both included and edited a version of the earlier prophecies along with his own, intending from the start that they should be read togather as a complete whole. This innovative and scholarly work, which sheds much new light on some of the more neglected passages, has had significant implications for future work on this much-loved prophetic book.