This paper presents a critical review of research on the use of code-switching as an instructional strategy in the teaching and learning of foreign or second language in bilingual contexts. Necessitated by the emerging and existing body of negative criticisms about its interference with the target language acquisition, this library-based paper sets out to critically review the use of code-switching to fathom its support as a crucial teaching and learning tool for language instruction, particularly in English language teaching and learning environments. This paper takes a qualitative inquiry that draws arguments primarily from library documentation. It particularly draws inferences from various theoretical orientations and empirical evidence within the confines of second or foreign language acquisition underpinning the fundamental use of code-switching in foreign or second language classrooms. Specifically, the paper attempts to theoretically justify the utilization of code-switching particularly in relation to its rationales and functions and, most significantly, its pedagogical implications to the process of second or foreign language teaching and learning. It ends with some suggestions on how teachers should take advantage of its availability and consistently maximize its use in bilingual classrooms.