The Agency for Healthcare Research and Quality (AHRQ) Quality Indicators (QIs) are a set of four indicator modules that use hospital discharge data to reflect quality of care and access to care. Three of the modules focus on in-hospital care, specifically procedure volume, in-hospital mortality and procedure utilization (Inpatient Quality Indicators, IQIs), complications of care (Patient Safety Indicators, PSIs) and potentially preventable complications and iatrogenic events for pediatric patients treated in hospitals (Pediatric Quality Indicators, PDIs). One module, the Prevention Quality Indicators (PQIs), focuses on area-level access to quality care as reflected by inpatient admissions for specific conditions. The indicators, originally developed by collaboration between Stanford University and University of California at Davis, under contract with AHRQ, are widely used by researchers, state data organizations, hospital associations, hospitals, state Medicaid agencies and the Centers for Medicare and Medicaid Services (CMS). The indicators are used for quality improvement, research, public comparative reporting, health care planning and value-based purchasing. This project supports scientific development and refinement of the AHRQ QIs.