The clinical microsystem puts medical error and harm reduction into the broader context of safety and quality of care by providing a framework to assess and evaluate the structure, process, and outcomes of care. Eight characteristics of clinical microsystems emerged from a qualitative analysis of interviews with representatives from 43 microsystems across North America. These characteristics were used to develop a tool for assessing the function of microsystems. Further research is needed to assess microsystem performance, outcomes, and safety, and how to replicate "best practices" in other settings.