Over the last 10 years, Computer-Supported Cooperative Work (CSCW) has identified a base set of findings. These findings are taken almost as assumptions within the field. In summary, they argue that human activity is highly flexible, nuanced, and contextualized and that computational entities such as information sharing, roles, and social norms need to be similarly flexible, nuanced, and contextualized. However, current systems cannot fully support the social world uncovered by these findings. In this article I argue that there is an inherent gap between the social requirements of CSCW and its technical mechanisms. The social-technical gap is the divide between what we know we must support socially and what we can support technically. Exploring, understanding, and hopefully ameliorating this social-technical gap is the central challenge for CSCW as a field and one of the central problems for human-computer interaction. Indeed, merely attesting the continued centrality of this gap could be one of the important intellectual contributions of CSCW. I also argue that the challenge of the social-technical gap creates an opportunity to refocus CSCW.