Since the Cambridge Science Festival launched in 2007, communities across the United States have experimented with the science festival format, working out what it means to celebrate science and technology. What have we learned, and where might we go from here? The Science Festival Alliance has supported and tracked developments among U.S. festivals, and this symposium will present key findings from three years of independent evaluation. While science festivals have coalesced into a distinct category of outreach activity, the diversity of science festival initiatives reflects the unique character of the regions in which the festivals are organized. This symposium will consider how festivals generate innovative public programming by adapting to local conditions and spur further innovation by sharing insights into such adaptations with other festivals. In 2013, more science festivals are expected in the United States than ever before. We will therefore conclude with a discussion of the implications of a dramatic increase in future festival activity for the United States.