This inter-disciplinary book is the first in an Irish context to address issues connected with the 'super-diversifying' of language and society engendered by recent and historical migrations. It analyses novel data from interviews with allochthonous and autochthonous groups of monolingual and plurilingual youngsters living in Northern Ireland. A key aim is to test models within second language acquisition and language variation and change research. Another goal is to examine the extent to which distinctive migratory trends generated changes in the language ecologies of communities on the island of Ireland as well as globally in regions where the Irish settled intensively from the 1700s. The book also compares contemporary migratory experiences with historical records to further our understanding of the dynamics of identification through language across time. The first-ever book devoted to all aspects of the sociolinguistics of globalization and migration in Northern Ireland will be welcomed by scholars interested in the consequences for ethnolinguistic vitality of large-scale population movements. It could not be more timely given the fact that 2.5 million sought asylum in Europe alone during 2016, greatly enhancing its diversity.