Ideally, legibility of the built environment is an issue where the interests of users and designers coincide: designers should care about users' positive experiences, and users' experiences are influenced by spatial stimuli. This Special Issue examines the spatial cognition of the built environment from the perspective of the user and the designer. It showcases current research examining how people behave in the built environment.The design and cognition of the built environment is an area that spans a number of disciplines, including architecture, psychology, geography, computer science, linguistics, complexity, and artificial intelligence. The interchange between these different domains of knowledge has led to the rise of various techniques, methodologies and tools; a key cross-over point is between architecture and psychology (Dalton, Hölscher, & Turner, 2012). This Issue examines approaches dedicated to the analysis and simulation of how individuals interact with their environment, through linking the structure of the environment with user behaviour.This Special Issue was born out of the "Design Cognition and Behavior: Usability in the Built Environment" workshop (Emo, Al-Sayed, & Varoudis, 2014) hosted during the Spatial Cognition 2014 conference in Bremen, Germany. Forty scientists and practitioners including architects, psychologists, cognitive scientists, and computer scientists came together to discuss the latest research on the behavioural aspects of human spatial cognition. The workshop highlighted the need for spatial cognition research to address its potential for innovation in the design of the built environment.One way of approaching this is through evidence-based design, which brings together the standpoint of the designer and the end-user. A designer is trained to anticipate the usage of a building or urban space, by considering how the end user will perceive and behave in the environment. Thus perceptual, cognitive and behavioural processes come together in the proposed design. The analysis of how individuals and groups interact with the built environment feeds directly into evidence-based design. The use of virtual experiments has been used extensively in the context of built environment modelling (see for example an early study by Dalton, 2001), and in the context of design using agent-based models (Maher & Gero, 2002), but there remains the need to extend the scope of these experiments and explore the use of hybrid worlds, where elements of both real and virtual worlds might be combined.Innovation in the design of the built environment can be supported with technical tools, analyses, and empirical models. These should not be alienated from users' experiences; the interaction between people and the built environment should be at the very essence of any modelling or design approach. Such an approach was theoretically articulated in the man-environment paradigm (Hillier & Leaman, 1973), and is embedded in the representational schemes and theoretical propositions of space syntax (Hillier, 1996(H...