This volume argues that language, ethnicity, and identity are defined by the circumstances under which they are created. The foundational chapter by Joshua A. Fishman describes how language, ethnicity, and identity are variable and changeable. The essays in the first part of the Handbook view language and ethnic identity through the lenses of sociolinguistics, psychology, anthropology, politics, and economics. These essays address important topics such as diasporic languages, language and ethnic identity near state borders, and the education of Indigenous peoples, language minorities, and the Deaf. The second part of the Handbook views language and ethnic identity through a regional perspective, embarking on a journey through Europe, the Americas, Africa and the Middle East, and Asia and the Pacific. Drawing on both historical and up-to-date accounts, these chapters examine the relationship between constructions of language and ethnic identity and constructions of nation-states. Although the volume offers considerable sophistication in the treatment of language, ethnicity and identity, it has been written for the non-specialized reader, whether student or layperson. Written by well-known scholars in their fields, the contributions offer a list of reference to steer readers to crucial further readings, as well as questions for further reflection and inquiry.