This paper summarizes 10 years of evidence of the effectiveness of collaborative improvement in improving health outcomes and compliance with health care standards. The study found that improvement collaboratives achieved large increases in compliance with health care standards—and in some cases in health outcomes—across all care areas addressed, regardless of the baseline level of quality. Findings provide compelling evidence that collaboratives can improve performance relatively rapidly. The analysis also suggests that moving beyond 80% performance requires system redesign to make high quality the routine. By achieving significant, sustained improvements in compliance with standards and outcomes, collaborative improvement is a viable tool for health systems strengthening in developing countries (2009, 48 pages).