This chapter offers a comprehensive exploration of semantics and pragmatics in the Thai language, emphasizing how meaning is constructed, interpreted, and influenced by context. The chapter is divided into two main sections. The first, on semantics, covers lexical, compositional, and contextual semantics, illustrating how Thai words and phrases derive and shift meaning based on structure and usage. It examines phenomena such as polysemy, synonymy, antonymy, homophones, homographs, ambiguity, and idiomatic expressions. The analysis includes detailed examples demonstrating how morphemes combine and how meaning can be altered by word order, context, and particles. The second section focuses on pragmatics, analyzing how meaning is shaped by social interaction. It addresses pragmatic functions such as requesting, apologizing, and expressing gratitude, and explores politeness strategies, honorifics, indirectness, euphemisms, and stancetaking. Particular attention is paid to how cultural norms and social roles influence language use in Thai communication. Through the integration of theoretical perspectives and practical examples, the chapter equips learners with the linguistic and cultural knowledge needed for effective, respectful, and contextually appropriate communication in Thai.