A growing conceptual and empirical literature is advancing the idea that language extends our cognitive skills. One of the most influential positions holds that language – qua material symbols – facilitates individual thought processes by virtue of its material properties (Clark, 2006a). Extending upon this model, we argue that language enhances our cognitive capabilities in a much more radical way: the skilful engagement of public material symbols facilitates evolutionarily unprecedented modes of collective perception, action and reasoning (interpersonal synergies) creating dialogically (...) extended minds. We relate our approach to other ideas about collective minds ( Gallagher, 2011, Theiner et al., 2010 and Tollefsen, 2006) and review a number of empirical studies to identify the mechanisms enabling the constitution of interpersonal cognitive systems. (shrink)