Universities' increasing applications of science and technology to address a wide array of societal problems may serve to thwart democratic engagement strategies. For emerging technologies, such challenges are particularly salient, as knowledge is incomplete and application and impact are uncertain or contested. Insights from science and technology studies (STS) are incorporated to examine the challenges that emerging technologies present to public engagement. Four distinct case summaries of public engagement in the emerging fields of nanotechnology and bioenergy are presented to demonstrate how the emergent character of the technology can stifle engagement. Specifically, the article explores issues related to emerging technologies and (1) defining and engaging with publics, (2) experiential variability among publics, and (3) frame contests. The goal is to sensitize engagement scholars and practitioners to these challenges as a way to minimize obstacles or tensions that may do harm rather than bolster meaningful and democratic engagement processes.