This course aims to help students understand how humans acquire both their first language (L1) AND a second language (L2). It provides an overview of major linguistic research on language learning, including how children AND adults develop linguistic knowledge such as phonology, morphology, AND syntax, as well as how communicative competence emerges through interaction. The main focus will be on second language acquisition (SLA), examining how learners construct interlanguage systems AND how linguistic, psychological, AND sociocultural factors influence learning. The course will also discuss how SLA research can inform effective L2 language teaching AND learning practices.