The purpose of this study is to explore Vygotsky’s contribution to the socio-cultural theory in the field of education in general, and applied linguistics in particular. The study aims to elaborate the impact of social-cultural theory in the existing body of literature. The study also reviews implications and applications of socio-cultural theory in second language acquisition (SLA). Moreover, this study also critiques the basic concepts of the theory and how far these concepts have been implicated in the domain of research. The central focus is to explore and to critically understand central ideas such as Zone of Proximal Development, mediation, scaffolding, internalization, and private speech. The socio-cultural theory focuses on what learners learn and the solution to their learning problems. Socio- cultural theory has made a great effect on learning and teaching languages. It also regards learning second language as a semiotic process where participation in socially mediated activities is very important (Ellis, 2000). Vygotsky (1987) singled out and studied the dynamic social surroundings which indicate the connection between teacher and the child. Moreover, he focused on the social, cultural and historical artifacts which play a pivotal role in the children’s cognitive development as well as their potential performance. The study concludes with the idea of Williams & Burden (1997) that socio-cultural theory suggests that education should be associated with learning to learn and making learning experiences meaningful and relevant to the learner. The study also suggests some pedagogical implications and offers teaching and learning practices in relation to socio-cultural theory.