This book explores the interaction between three key aspects of everyday life—language, writing, and mobility —with particular focus on their effects on language contact. While the book adopts an established view of language and society that is in keeping with the sociolinguistic paradigm developed in recent decades, it differs from earlier studies in that it assigns writing a central position. Sociolinguistics has long concentrated primarily on speech, but Florian Coulmas shows in this volume that the social importance of writing should not be disregarded: it is the most consequential technology ever invented; it suggests stability; and it defines borders. Linguistic studies have often emphasized that writing is external to language, but the discipline nevertheless owes its analytic categories to writing. Finally, the digital revolution has fundamentally changed communication patterns, transforming the social functions of writing and consequently also of language.