This is a definition of labour market segmentation in the Thematic Encyclopedia of Regional Science. This thematic Encyclopedia explores the multifaceted world of regional science, presenting a systematic and coherent overview of its central topics. It highlights the interdisciplinary nature of the field, examining the wide range of concepts, theories, methods and models that shape spatial-oriented approaches to the social sciences. Contributions from expert scholars delve into key aspects of regional science, from urban poverty and natural resource management to smart cities and AI. Highly accessible entries cover the definition, history, theoretical background, and applications of each topic, as well as avenues for future research.