This document discusses theories of second language acquisition and their influence on English language teaching. It examines key theories that have attempted to influence SLA over time, from behaviourism to cognitive approaches. While early theories focused on linguistic and psycholinguistic factors, more recent theories emphasize the importance of social and sociolinguistic factors in language learning. The document also discusses factors that influence the amount and type of language input learners receive, and how this impacts the development and success of second language acquisition.