Multilingualism, language contact, and urban areas An introduction Ingrid Gogolin, Peter Siemund, Monika Schulz, and Julia Davydova Te title of this volume describes a key feature of modern urban areas: an increas- ingly multilingual composition of their populations, and the consequent encoun- ter of language diversity. Te driving force underlying this dramatic development is migration. Te number of languages that exist in one and the same region has increased immensely over the last fve decades – yet, mature, research-based knowledge about this phenomenon and its consequences for language develop- ment and learning, language vitality and attrition, as well as language use and change is scarce. Tis is largely due to the fact that research on the causes and consequences of increasing linguistic diversity addresses a wide range of topics and perspectives. Tus, traditional boundaries between the disciplines that are concerned with language and linguistic diversity need to be crossed. Te complex- ity of issues that must be observed and analyzed calls for joint research activities from diferent disciplinary perspectives. Te contributions to this volume rep- resent an attempt to initiate exchange between researchers from a wide range of specializations and disciplines, exhibiting a shared interest in learning more about linguistic diversity. In order to explain the social reality that provides a framework for research on linguistic diversity in urban areas, we begin this introduction by presenting some facts and fgures about the levels of actual migration, while, at the same time, highlighting its linguistic ramifcations. In the subsequent paragraphs, we will look at the notions constituting the focal points of research addressed in the chapters of this volume.