The Institute for Healthcare Improvement's Global Trigger Tool has been used to quantify the incidence of preventable harm in seminal studies. This study describes how a large health system used the Global Trigger Tool to identify causes of preventable harm, track adverse event rates over time, and guide improvement efforts. Through a standardized assessment and dissemination process, this health system achieved reductions in preventable adverse events across its 25 hospitals over a 2-year period. Although the Global Trigger Tool is widely used, concerns have been raised about its reliability, and it is generally recommended that organizations should use multiple methods of detecting safety hazards to gain a comprehensive picture of patient safety.