What’s the value of doing things together? Human sociality is perhaps the distinguishing characteristic of our species, the foundations of which lie in direct face-to-face social interaction. Much research has been directed toward uncovering the psychological mechanisms and processes underpinning coordinated social action, but what remains to be described are the precise ways that participants in real life activities decide to act together or separately. Rather than relying on laboratory experimentation, the proposed research will use naturally occurring social activities to specify participants’ understandings of the utility and appropriateness of joint action. In particular, I will examine a setting where participants must recurrently appraise the relevance of collaborative action: building construction sites. I will undertake three studies using a combination of qualitative and quantitative methods to uncover how participants who are committed to a common project detect and act upon opportunities for closely interlocked action. This project serves as an empirical advancement in research on social interaction by articulating the connections between these fundamental modes of human conduct. The findings of this project will also resonate with researchers of pragmatic disorders, workplace organization, and human-robot interaction. (186 words)