Abstract. Language acquisition is a foundational area of study within linguistics, psychology, and education, as it seeks to explain how humans learn language both their native tongue and additional languages. This article provides an in-depth exploration of the major theories of language acquisition, highlighting their historical development, core principles, and implications for teaching and learning. Drawing from a broad interdisciplinary base, the article examines both first language acquisition (L1) and second language acquisition (SLA), comparing their processes and underlying cognitive mechanisms. The study begins by exploring classical theories such as Behaviorism, championed by B.F. Skinner, which posits that language learning is a result of habit formation through stimulus-response reinforcement. This is contrasted with Noam Chomsky’s Nativist Theory, which introduced the concept of a universal grammar and the idea that humans are biologically predisposed to acquire language through an innate Language Acquisition Device (LAD). Further, the Cognitive Theory, as proposed by Jean Piaget, emphasizes the role of mental processes and developmental stages in language learning. Contemporary approaches such as Stephen Krashen’s Monitor Model, with its five key hypotheses, especially the input hypothesis, are discussed for their relevance in second language learning contexts. The article also explores Social Interactionist Theories, notably Lev Vygotsky’s work, which underscores the importance of social context, interaction, and scaffolding in the development of linguistic competence. Additionally, newer theories such as Connectionism and Emergentism are introduced, offering insights into how language structures emerge from the interaction of linguistic input with cognitive processes without invoking innate grammatical rules. The article examines the strengths and limitations of each theory, analyzing how they apply to real-world learning environments and language instruction strategies. By synthesizing various perspectives, this article emphasizes that language acquisition is a complex, multifaceted process influenced by a combination of biological, cognitive, and environmental factors. It highlights the need for educators to understand the theoretical foundations of language learning in order to design effective pedagogical practices that cater to diverse learners. Ultimately, the study aims to contribute to the broader discourse on language development by offering a comparative overview of major theories and their educational implications in the field of applied linguistics.