Migration, among the most important sociocultural phenomena of contemporary global societies, is complex, dynamic, and multifaceted. At the heart of migration is language, the indispensable agent of migration. Hence, in this article, a new sub-discipline of linguistics is presented, and that is 'migration linguistics'. It is the interdisciplinary and multidimensional study of the various aspects of language within the dynamic process of human mobility. And a linguistic theory of migration postulates that: (1) Language is an essential element in the migration process; (2) an individual's acquisition, learning, and use of language significantly changes as a result of migration; and (3) migrants must be understood in the languages they can use, taught the destination language, and provided basic and essential services understandable to them. The interdisciplinary nature of this new sub-discipline of linguistics is enriched by a variety of approaches and methodologies in solving issues relative to language in the context of migration.