This is in fact an attempt to compile lecture notes on the most popular and useful theories and concepts outlined on language in general, and Second/Foreign language learning and teaching in particular. It includes the sum and substance of the theories of language outlined by Ferdinand de Saussure, Vygotsky, Noam Chomsky, Michael Halliday and Hassan. Also, it presents precisely the theoretical and experimental views on SL/FL by scores of scholars and linguists such as Selinker, Stephen Krashen, Dell Hymes, H.W. Widdowson, Peter Skehan, Cummins, Rod Ellis, Lantolf, David Crystal, Candlin, Merrill Swain, Leo Van Lier, Jack Richards, Zoltan Dorneyi, Richard Schmidt, S. Larsen-Freeman, Kumaravadivelu, Chilukuri Bhubaneswar, Howard Gardener, McIntyre, S'fard, Douglas Brown, David Crystal etc. Attempts have been made to make the chapters precise and useful to meet the needs of teachers and students for basic references at tertiary level studies related to classroom teaching, note making and preparing for exams in SL/FL acquisition.