This document summarizes a paper presented at the 12th International Public Communication of Science and Technology Conference in April 2012. The paper examines how publics form around emerging technologies, distinguishing between "upstream" and "downstream" engagement. Upstream engagement occurs early in technology development when implications are unclear, allowing organizers more control over publics. Downstream engagement happens when technologies are tangible, so publics are more likely to emerge from civil society in response to specific impacts. The paper uses two Scottish renewable energy cases to illustrate how publics emerge in response to local wind farms and concerns over global biomass sourcing. While organizers can shape upstream publics, downstream technologies make wider socio-technical networks and uninvited publics more