The introduction to this volume aims to clarify some key concepts, in particular the concept of urban segregation, and to introduce the three-part structure of the book. Through the introduction of these – interrelated – parts, the most compelling segregation debates are outlined. Such debates come to the fore in Part I through a ‘world tour’ across six continents, sixteen countries, and a multitude of cities, confronted with pressing segregation questions across a range of institutional contexts. The introduction to Part II confronts the various domains of segregation that are dealt with in the book. Beyond the more familiar but still imperative residential domains, segregation in public space, in education and with regard to human relations with the ‘natural’ environment are also addressed. The dimensions of such segregation dynamics include race, class, and other demographic and cultural dimensions. Part III then turns to new issues and approaches fundamental to the practice of measuring, conceptualising and framing segregation. This introductory chapter concludes with an initial impression of the key collective findings of this volume, while a more elaborate discussion of these is found in Chapter 24. Attention is given to the impact of varied local or regional contexts, to historically grown legacies connected to urban segregation, and to the continued significance of welfare regime types for understanding segregation.