Written for students encountering the topic for the first time, this is a clear and practical introduction to second language acquisition (SLA). It explains in non-technical language how a second language is acquired; what the second language learner needs to know; and why some learners are more successful than others. The textbook introduces in a step-by-step fashion a range of fundamental concepts such as SLA in adults and children, in formal and informal learning contexts, and in diverse socio-cultural settings and takes an interdisciplinary approach, encouraging students to consider SLA from linguistic, psychological and social perspectives. Each chapter contains a list of key terms, a summary, and a range of graded exercises suitable for self-testing or class discussion. Providing a solid foundation in SLA, this book is set to become the leading introduction to the field for students of linguistics, psychology, and education, and trainee language teachers.