This commentary by Dr. Donald Berwick, president of the Institute for Healthcare Improvement, addresses the growing tension between "needing to improve care and knowing how to do it." Berwick argues that traditional tenets of evidence-based medicine, such as relying on randomized trials to demonstrate evidence of effectiveness, are less useful when examining the effect of quality improvement interventions, given the complexity of hospital systems and local environments. Berwick suggests four changes in the approach to evidence-based evaluation of patient safety interventions that, if adopted, may bridge the gap he perceives between academic medicine and front-line providers. Dr. Berwick discussed his career in patient safety in an AHRQ WebM&M conversation in 2005.