Recent research has made significant discoveries which have greatly enhanced our understanding of how Castellio was read, and by whom, through to the end of the Enlightenment. There have been numerous attempts to trace the readership of Castellio’s works, but this task is fraught with difficulties; doubtless the uncovering of further information or the discovery of previously unknown connections will one day enable us to have a clearer picture of Castellio’s posthumous influence. The major difficulty is that the evidential basis for such an undertaking remains problematic. For the most part it is limited to a collection of citations, commentaries, reprints and editions of texts in which Castellio’s name is mentioned. Clearly, many who read Castellio did not wish to be openly identified with his ideas. We must not forget that until the eighteenth century, Castellio remained a highly controversial author, and that the mere mention of his name could have detrimental consequences for a writer, publisher or printer. Thus one often finds in the literature on toleration from the seventeenth and eighteenth centuries strong echoes of Castellio’s thought without any precise references to his works.