Our understanding of the history and development of Arabic is greatly challenged by the dearth of sources. Most scholars who have undertaken this task in the past have relied almost exclusively on data from the Arabic grammatical tradition. These sources claimed that Arabic originated as the language of the Bedouin of the central and southern Arabian Peninsula, and was only introduced to the settled areas of the Levant and Mesopotamia following the Islamic conquests. In this dissertation, I argue that there is no scientific basis for this view. The first chapter of part one of the dissertation begins with an examination of the evidence for Arabic in the Fertile Crescent from the pre-Islamic period. This evidence suggest that Arabic was part of the linguistic milieu of the Levant and Mesopotamia as early as the Iron Age. Next, I discuss the Arabic grammatical tradition and how it has influenced the production of modern theories regarding the history of Arabic. Chapter two engages in a comprehensive study of the evidence for pre- and early- Islamic Arabic from the Arabic grammatical tradition and the pre-Islamic epigraphic and papyrological sources. The first part of this dissertation concludes with a comparison of the data from both sources and a preliminary classification. Part two begins by arguing that, in light of the results of part one, there is no "a priori" reason to assume that the modern northern dialects of the Levant and upper Mesopotamia were introduced from the Peninsula following the Islamic conquests. The next two chapters engage in the reconstruction of the common ancestor of the contemporary and ancient northern dialects though the application of the comparative method. Chapter three identifies a group of shared genetic isoglosses between the Syro-Palestinian dialects, the Q[schwa]ltu dialects, and, where possible, the ancient northern sources. I then reconstruct the phonology of Proto-Levantine Arabic by comparing relic modern dialects to the papyrological and epigraphic dialects. In the same way, chapter four reconstructs morphology. Chapter five concludes with a summary of the results and a preliminary sub-classification of the pre-diasporic Arabic dialects. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]