Human cognition reflects the necessities of living in social groups transmitting cultural knowledge. Human minds are, richly and deeply, social minds. Working together we aim to better understand social minds by testing a new integrated theory with innovative methodologies.Joint action and communication both build and exploit common ground. At a basic level common ground is tied to shared perceptions and shared action repertoires allowing joint activities. At a second level, established through ostensive communication, common ground includes also general knowledge of enduring relevance. These two levels have been studied separately. We hypothesize that joint action exploits forms of ostension found at the second level, and that ostensive communication draws on forms of coordination found at the first level. Through our integrated study of the two levels we aim to redefine the relation between coordination, communication, and cultural transmission.Our common program will close gaps between research that has focused on the processes and representations that enable joint action (Call, Knoblich) and research that has addressed intentional communication and its role in cultural transmission (Gergely, Sperber). It will integrate the study of a) embodied cognitive mechanisms for interpersonal coordination, b) shared intentions and shared task representations, c) ostensive communication, d) natural pedagogy, and e) how all of the above provide the micro-mechanisms of cultural transmission.Integrating the four PIs’ research programs will also lead to methodological synergies. We will develop and use in a converging manner experimental procedures for the comparison of infant, children, human adult and primate data, models of cultural evolution, and novel ways of eliciting and using anthropological evidence, leading to a transfer of methodological knowledge and practices across fields.