The Thesis is an attempt to reconstruct the dialect geography of the North-Arabian language area before its enlargement by the Islamic Conquests in the seventh century A.D. It is based on statements by native philologists of the second to fourth centuries of the Hijra, as recorded in their own works and in later dictionaries, grammars, and commentaries. The data are examined in the light of phonetic and linguistic theory, and the geographical extension of the phenomena ascertained, wherever this is possible. The results of the geographical investigations are illustrated by a number of maps. Similarities between the different dialects and the other Semitic Languages on one hand, and the modern Arabic colloquials on the other, are pointed out, though no systematic treatment of these relationships is aimed at. CONTENTS: Reasons for the neglect of the dialects by the native philologists - The axiom of the identity of the Classical language with the Hijaz dialect - Nature and quantity of the available material The sholars from whom observations on the dialects are reported - Their scientific background - The value of their data - Discussion of some early works - The secondary sources - Their attitude to the dialects - Some sources of false data - Former studies of the subject by modern European and Oriental scholars - Methods of the Thesis - Map of the tribes dealt with. Discussion of the material pertaining to phonetics, morphology, and syntax of the following dialects: Yemen - Hudhail - Azd Sarat - Hijaz - Tayyi - Qudaa - The Eastern Group - Temim - Asad - Rabi'a Uqail - The Central dialects. The stratification of the dialects - The dialects and the modern colloquials - The basis of the Literary idiom. Alphabetical list of ca, 750 purely lexicographical data for all dialects - The data for the dialect of Jurhum - Data for South - Arabian dialects.