 Pradeu takes the boundary established and maintained by the immune system as the boundary of the organism. On Pradeu’s view, organisms are inherently heterogeneous, given the collaborative nature of the microbial and macrobial worlds articulated in Microbialism. To put it slightly differently, the true organisms delineated by Pradeu’s immunity criterion are holobionts constituted by a macrobial organism and all and only those microbes at least tolerated by its immune system. This criterion provides a way to individuate organisms as holobionts, and the resulting view constitutes one way to constructively respond to the challenges of Microbialism and Eliminativism. Whether holobionts are best thought of as organisms or evolutionary individuals at all (Skillings 2016), or whether Pradeu’s view in particular can resolve the putative “tension in seeing symbionts as both organisms themselves and also parts of larger organisms” (Godfrey-Smith 2016c: 782), remain live issues.