The notion of how Arabic expanded through North Africa and the Iberian Peninsula and became the major language in al-Andalus has occupied specialists in the field of Arabic linguistics for decades. The absence of primary sources and historical data has prevented Arabic linguists from finding satisfactory explanations to this question. My dissertation is concerned with the study of the geographical diffusion of the Arabic language through North Africa and the Iberian Peninsula during the first centuries of the Islamic presence in the region. In particular, I study the mechanisms by which this language was transmitted with a special focus on the cities of Kairouan, Cordoba, and Fez. Most scholarship on this topic has relied almost entirely on the analysis of common linguistic features shared by Arabic dialects to explain how this language evolved over time in the Western Mediterranean. However, I argue that by singularly focusing on linguistic factors our understanding of this process has been limited. I draw on the notions of “population movements” and “trade” in an attempt to better understand the processes by which the Arabic language was transmitted through the Western Islamic world. Moreover, I hypothesize that the nature of population shifts and trade networks established between the main North African centers and al-Andalus constituted the precise channels through which Arabic in its different forms, dialectal and standard, spread to the Iberian Peninsula.