Flash mobs have spread, like wildfire, across the globe in recent years fuelling new uses of urban public space. The media has wondered if these events are simply pointless pranks, creative public performances, or mass social experiments in community building. Existing research emphasizes only the vital role of digital communications technology in the mobilization process. In contrast, this analysis shows through a broad range of examples from New York, London, Berlin, Budapest to Tokyo that these nascent forms of collective action are also important to examine because they provide insight into the intersection and interaction between new communications media and changing uses of physical urban space. It situates flash mobs in a historical context, constructs a basic typology of flash mob activity based on extensive Internet research, and theorizes it as a new form of sociability. It also explores how these examples of urban creativity have inspired commerce and politics to rediscover urban space, increasingly borrowing the organizational techniques of flash mobs in marketing campaigns and social protests.