This text brings together well-known scholars in two relatively distinct fields (language acquisition and language socialization) and from a variety of orientations within applied linguistics - psycho and sociolinguistics, anthropological linguistics, educational linguistics - to describe language development from a relational perspective. The notion of ecology offers a convenient metaphor for the complex variational processes that take place within individuals and between individuals and their social and cultural environment, as they attempt to learn the language of the other. The theme of ecology affords a fresh look into phenomena not encompassed by language acquisition or language socialization research alone. It puts into question traditional ways of looking at time, space, subjectivity, identity in the acquisition of another language and its use in a variety of social contexts. For language teachers and educators, this book attempts to eschew traditional dichotomies such as language acquisition vs. language use, and to capture the complex and holistic nature of language learning and teaching.