Written for students encountering the topic for the first time, this introduction 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 logically introduces a range of fundamental concepts--such as SLA in adults and children, formal and informal learning contexts, and diverse socio-cultural settings. It takes an interdisciplinary approach, encouraging students to consider SLA from linguistic, psychological and social perspectives.