The Book of Isaiah is one of the three books of the second part of the Nevi’ im, the Major Latter Prophets, from three parts of the Hebrew Bible. Some of scholars believe that the entire sixty and six chapters of the Book of Isaiah are the product of a single author, the historical Isaiah of Jerusalem, by citing the linguistic, stylistic, and theological similarities. But majority of scholars divide it into three distinct parts, by citing the historical, linguistic, stylistic, and theological differences and assign them, respectively, to First Isaiah, Second Isaiah, and Third Isaiah. This article, written in descriptive and analytic way, deals with the historical background of the unity of authorship or the multiple authorship of this book, and the factors of the adherents of each of these views. Adherents of the unity of authorship consider use of the concepts such as a highway, Zion, the holy one of Israel, and pangs of a woman in travail throughout the book as justifying their views. Adherents of the multiple authorship respond to it by saying Second Isaiah, and Third Isaiah were the followers of Isaiah and then these similarities come from this point.