This module investigates some of the theoretical aspects to speech production and sound structure across the World's languages. We will spend time discussing and evaluating different frameworks for modelling phonetics and phonology, for example generative and usage-based approaches. Then, we will examine some case-study areas which challenge existing theories, for example intonational phonology and the study of historical sound change. This module aims to contribute to questions such as 'How are groups of sounds structured so that we can understand language?' or 'How are sounds stored and processed in the mind?'