Language allows humans to act cooperatively, to plan, and to remember. It is the prime factor in the constitution of groups as well as a major barrier between groups. Language policy and planning is rarely just about language; it always has political, social and ethical dimensions. This is a comprehensive advanced textbook, covering not only language learning imposed by economic or political agendas but also language choices entered into freely for reasons of social mobility, economic advantage or group identity. The first part of the book reviews the development and role of standard languages in the construction of national communities and identities. The second part examines the linguistic accommodation of groups in contact, major lingua francas and the case of 'International English'. The third section explores reactions to nationalism and globalization, with some attention to language rights. The book further deals with methodological problems of working in this interdisciplinary area, and provides detailed illustrations from a range of countries and communities.