In my dissertation, I explore the remarkable talent of human beings to modify and co-opt resources of their material and socio-cultural environment, and integrate them with their biological capacities in order to extend their cognitive prowess. First I clarify and defend the claim—known as the extended mind hypothesis—that some episodes of our cognitive processing literally stretch beyond our heads and bodies to encompass aspects of the environment. Since much of distinctively human cognition occurs when we think in groups, I further argue that the bias of this hypothesis to view cognition as an essentially solitary—albeit naturally or technologically extended—activity is misplaced. Hence I re-deploy the conceptual framework of cognitive extensions to establish a scientifically respectable version of the group mind hypothesis—the idea that some groups have cognitive properties that differ from those had by their members. The central thesis of my dissertation is that minds are not confined to the boundaries of the individual.