This Episode provides a theoretical background to language acquisition, distinguishing between first and second language learning. It critically examines various theories, ranging from behaviourism and structuralism to cognitive and discourse theories, ultimately advocating for a Universal Grammar-based cognitive interactionist approach to second language acquisition. The chapter further explores the implications of this perspective on pedagogy, including curriculum goals, teacher roles, error treatment, the importance of comprehensible input, the learning environment, and materials. It also discusses individual learner differences, multiple intelligences, and the whole language approach in the context of second language acquisition in India.