Space syntax is a set of theories and techniques about buildings and cities and how they function, rooted in a theory of society and space that originated at the UCL Bartlett School of Graduate Studies in the 1970s. The ability of space syntax methods to objectively measure the physical andspatial attributes of cities in relation to patterns of human activity has led to hundreds of projects, covering subjects as diverse as the relationship between burglary and housing layout, the architecture of Inuit snow houses and visitor movement in museum layouts. This special issue of Progress in Planning will focus on some of the contributions made by 'space syntax' to a subject that is becoming of increasingly wide interest: the relationship between urban form and social segregation.The issue begins with an overview by Bill Hillier and Laura Vaughan of space syntax as a theory of the city and a set of techniques for analysing its spatial form. This is followed by a chapter by Laura Vaughan that analyses poverty and spatial form in Charles Booth's maps of 19th century London, describing new findings relating to the persistence of poverty areas and immigrant 'ghettos' and proposing a spatially defined line of poverty, distinguishing between poor, spatially segregated streets and more prosperous, spatially integrated streets. Following this, a chapter by Lars Marcus suggests that segregation is inherently a spatial problem. Hedemonstrates this through a detailed analysis of residential segregation and social integration in public space of housing estates constructed through the Swedish Million Homes Programme. In the penultimate chapter Ruth Conroy Dalton discusses segregation in the US context, through a study of social exclusion, transportation equality, transit equity and leisure trail use in Peachtree City, Georgia, showing that the accessibility of leisure trails coupled with the flexibility and relative affordability of electric golf carts, means that the level at which families and individuals are disadvantaged through their lack of access to public/private transport iseffectively lowered. The issue ends with conclusions regarding the future of segregation in the urban context and some recommendations for policy makers and urban planners.