 It is my honor to offer this replacement for the previous SEP entry on Poulain written by Desmond M. Clarke (1942–2016). In particular, my bibliography of Poulain’s works is based on his. In addition to the secondary literature cited and personal communication with many of the authors, my interpretations of Poulain’s thought are indebted to numerous discussions with Tuomas Parsio, the translator of Poulain’s De l’égalité into Finnish.