The success of interactive media architecture projects is contingent on the participation of the public. However, a fundamental question faced by designers of such systems is how open should their work be to public manipulation, while still providing adequate control so as not to compromise the design intent. This chapter take the position that control and freedom are negotiated constructions developed in real-time between the design’s intentions, the public’s desires for engaging it, and the existing protocols of behavior in public spaces. Questions that it poses include: What is information and how is it constructed? What is the relationship between control and freedom in interactive systems? What role can public participation play in its formulation? How can it be sustained? In response, it proposes an approach for underspecifying a design, in order to collectively construct both information and the public.