In learning languages, a distinction is usually made between mother tongues, second languages, and foreign languages. A mother tongue is the first language or languages one learns (or acquires) as a child. This book presents findings on language learning including the methodologies commonly used by behaviour analysts to teach verbal behaviour; the use of multimodal tools for pronunciation training in second language learning in preadolescents; and teaching health professionals about language barriers to improve health care disparities and outcomes.