Geopolitical borderlands such as the moving frontier of the Christian reconquest in medieval Iberia and today's mexican-U.S. border call to mind complex cultural and linguistic dimensions that internal nonbordering areas do not. Peoples living in border or liminal cultural areas are often characterized as having hard-to-define and multiple identities, a situation often reflected in their linguistic performances. Although political borders may be well defined, linguistic borders are not. On either side of political borders we find an overlapping and intermixing of languages within a small geographical space, and the contact between two or more languages along border areas has produced widely different linguistic outcomes, such as continued development of each individual language, language mixing or shift, or language extinction of at least one of the languages. The linguistic circumstances of Spanish and english along the mexican-U.S. border today in many ways parallel those of the border areas of medieval Iberia and the Arabic and Romance languages. Given the many similarities between Al-Andalus (711–1492 c.e.) and the Southwest, a comparative analysis of the sociolinguistic developments within Al-Andalus and those of the American Southwest may further our understanding of underlying linguistic processes that may contribute to or hinder the successful maintenance of languages in border areas.