Abstract. Language acquisition is a fundamental aspect of human development and has been the subject of extensive study across multiple disciplines, including linguistics, cognitive science, psychology, and education. Understanding how individuals acquire language, whether their first language (L1) or a second/foreign language (L2), is crucial for the development of effective teaching methodologies and learning environments. This paper provides an in-depth examination of the primary theories that attempt to explain the process of language acquisition. The Behaviorist Theory, pioneered by B.F. Skinner, emphasizes imitation, reinforcement, and habit formation. In contrast, the Nativist Theory, led by Noam Chomsky, argues for an innate, biological capacity for language learning, proposing the existence of a “language acquisition device” (LAD). The Cognitive Theory, influenced by Jean Piaget, highlights the role of mental processes and developmental stages in language learning, while the Social Interactionist Theory, associated with Lev Vygotsky, stresses the importance of social context and interaction in the acquisition of language.