Who or what makes innovation spread? Ten case-studies from Greco-Roman Antiquity and the early modern period address human and non-human agency in innovation. Was Erasmus the ‘superspreader’ of the use of New Ancient Greek? How did a special type of clamp contribute to architectural innovation in Delphi? What agents helped diffuse a new festival culture in the eastern parts of the Roman empire? How did a context of status competition between scholars and poets at the Ptolemaic court help deify a lock of hair? Examples from different societal domains illuminate different types of agency in historical innovation.