Interaction among strangers is a defining feature of urban life and one that contributes to vibrant urban environments. As a general rule, however, strangers would need a reason to interact with each other. This PhD project sets out to investigate social, cultural and physical-spatial factors that support interaction among strangers in urban public space. While the analysis of the empirical material will draw on American sociologist Erving Goffman’s classical theory of behavior in public places, the project also aims to test the part of this theory focusing on ‘engagements among the unacquainted’ in a contemporary, Northern-European setting. The main investigation will consist of a combination of qualitative methods, primarily detached and participant observation. Field work will be undertaken in six public spaces, i.e. public squares, of inner city Oslo.