The Book of Isaiah is the first of the Latter Prophets in the Hebrew Bible and the first of the Major Prophets in the Christian Old Testament. It is identified by a superscription as the words of the 8th-century BCE prophet Isaiah ben Amoz, but there is evidence that much of it was composed during the Babylonian captivity and later. Johann Christoph Döderlein suggested in 1775 that the book contained the works of two prophets separated by more than a century, and Bernhard Duhm originated the view, held as a consensus through most of the 20th century, that the book comprises three separate collections of oracles: Proto-Isaiah, containing the words of the 8th-century BC prophet Isaiah; Deutero-Isaiah, or "the Book of Consolation",, the work of an anonymous 6th-century BCE author writing during the Exile; and Trito-Isaiah, composed after the return from Exile. Isaiah 1–33 promises judgment and restoration for Judah, Jerusalem and the nations, and chapters 34–66 presume that judgment has been pronounced and restoration follows soon. While few scholars today attribute the entire book, or even most of it, to one person, the book's essential unity has become a focus in more recent research.

In Abrahamic religions, a messiah or messias is a saviour or liberator of a group of people. The concepts of mashiach, messianism, and of a Messianic Age originated in Judaism, and in the Hebrew Bible, in which a mashiach is a king or High Priest traditionally anointed with holy anointing oil.