Mauritania, a Muslim country the majority of whose population speaks Ḥassāniyya Arabic, is at the western edge of the Arabic-speaking world. At the birth of Islam, the western part of the Sahara was inhabited by Berbers, with Black African populations bordering their territories to the south and south-east. After the arrival of the Banī Maˤqil at the end of the thirteenth century, Arabic- and Berber-speaking groups coexisted more or less peacefully, the Arabic speakers achieving supremacy little by little, starting in the military and political sphere and ending with cultural and linguistic domination. But if the close contact between those groups made a deep impression on Zenaga Berber (resulting ultimately in its disappearance), Zenaga also contributed a number of its characteristics to the Ḥassāniyya Arabic dialect. This chapter reviews the different stages of Arabization and offers a historical reconstruction of Ḥassāniyya through an assessment of the features shared with other Arabic dialects.