This book provides a pioneering introduction to heritage languages and their speakers, written by one of the founders of this new field. Using examples from a wide range of languages, it covers all the main components of grammar, including phonetics and phonology, morphology and morphosyntax, semantics and pragmatics, and shows easy familiarity with approaches ranging from formal grammar to typology, from sociolinguistics to child language acquisition and other relevant aspects of psycholinguistics.