This article approaches social media from the theory of the religio-political practice of acclamation revived by Agamben and following twentieth-century social and political thought and theology (of Weber, Peterson, Schmitt, Kantorowicz). It supplements that theory by more recent political-theoretical, historical and sociological investigations and regards acclamation as a ‘social institution’ following Mauss. Acclamation is a practice that forms publics, whether as the direct presence of the ‘people’, mass-mediated ‘public opinion’, or a ‘public mood’ decipherable through countless social media postings. The article surveys issues of differential geographies of access, weighting of posts, value-creation, orality and gesture, algorithmic governmentality, and Big Data and knowledge production. It argues that social media constitute a public from a mass of individualized, private postings. It concludes that they make possible forms of political calculability and action, yet are continuous with ritual and liturgical elements of political life. This study contributes to an analytics of publicity.