The lecture will help familiarise yourself with the foundations and current key issues of second language acquisition (SLA). We will cover potential definitions as well as historical developments of SLA, its theories and models as well as their relevance for instructed language learning. In particular, the historical overview will look at behaviourist models, Universal Grammar, the Monitor Model, the interaction hypothesis, Processability Theory, skills acquisition, emergentism, the Declarative / Procedural Model, as well as Complexity Theory. We will then discuss the role of classroom instruction, input processing, output, the similarities between L1 and L2 acquisition and language transfer, the critical period for acquiring a second language, foreign language aptitude, learning strategies, the interlanguage system, and communication in the second language. There are no prerequisites for this lecture.