The study of how linguistic variation is acquired is considered a nascent field in both psycho- and sociolinguistics. Within that research context, this book aims at two objectives. First, it wants to help bridging the gap between researchers working on acquisition from different theoretical backgrounds. The book therefore includes contributions by both psycho- and sociolinguists, and by representatives of further relevant sub-disciplines of linguistics, including historical linguistics and dialectology. Second, in order to enable cross-linguistic comparison, the book brings together research carried out in different sociolinguistic constellations, as most obviously found in different language areas or different countries.