Against the backdrop of the imperatives for actors within the institutional framework of energy socio-technical systems to engage with the public, the aim of this paper is to consider interdependencies between the principles and practice of engagement and the nature of the imagined publics with whom engagement is being undertaken. Based on an analysis of 19 interviews with actors in the renewable energy industry, the paper explores how publics are imagined in the construction of the rationales, functions and mechanisms for public engagement. Three main themes are identified. First, the perceived necessity of engagement -which is not contingent on public responsiveness. Second, engagement is primarily conceptualised in terms of instrumental motives of providing information and addressing public concern. Third, preferences for engagement mechanisms were often a function of the specific characteristics attributed to imagined publics. Implications of this analysis for future engagement around siting renewable energy technologies are considered.