Exploring Innovation and Quality Improvement in Health Care Micro-Systems defines and describes health care micro-systems and analyzes characteristics that enable specific micro-systems to improve the quality of care provided to their patient populations. This study reports on structured interviews used to collect primary data from 43 micro-systems providing primary and specialty care, hospice, emergency, and critical care. It summarizes responses to the interviews about how micro-systems function, what they know about their level of performance, how they improve care, the leadership needed, the barriers they have encountered, and how they have dealt with these barriers.