As contemporary cities become environments supporting increasing media density, it is important to reexamine our understanding of the dynamics of public space. The transformation of media into geo-media, characterized by ubiquitous networks coupled to context-sensitive information, means that urban space is now subject to new geometries of power and opened to new forms of agency. Large-scale public screens are both one of the most visible signs of this trajectory, and a strategic site for its analysis. While the urban screenscape has often inspired futuristic cinematic scenarios, such as the dystopic city of Blade Runner (1982), the forms of spectatorship and social practice incubated by urban screens in fact differ significantly from those associated with cinema. Moreover, in a digital networked culture, urban screens have gained the potential to move beyond "ambient television" to play a more proactive role in initiating new collective interactions in public space. Drawing on the approaches and projects developed around several different sites for urban screens, this paper will examine the potential for urban screens to facilitate new modes of participation in the public spaces of networked cultures.