Health care disparities are the differences or gaps in care experienced by one population compared with another. Disparities have been noted in health outcomes, including clinical outcomes such as mortality, process measures in the health care system, and disease prevalence. By definition, a disparity in health care quality or health outcomes is not due to differences in the health care needs or preferences of the patient but to other factors. Such differences in health outcomes and their determinants are associated with certain social conditions and demographic attributes. Disparities that occur between identified populations are described by attributes such as race, ethnicity, language, sex, insurance status, socioeconomic status, and health literacy. These attributes and the disparities that may be associated with them are not mutually exclusive, and populations with disproportionately poor health outcomes often share multiple indicators of disparity. Despite what is known about disparities, it is not clear what strategies have the potential to improve the quality of care effectively and to reduce inequities for segments of the population. Quality improvement (QI) is a multidisciplinary, systems-focused, data-driven method of understanding and improving the efficiency, effectiveness, and reliability of health processes and outcomes of care. The QI process is designed to raise the standards of the delivery of preventive, diagnostic, therapeutic, and rehabilitative measures to maintain, restore, or improve the health outcomes of individuals and populations. Given the potential for QI strategies to improve the quality of care across the population, interest has developed in whether they might be used to reduce specific disparities, potentially by having an amplified effect among disadvantaged groups. For this report, we defined a QI intervention as a change process in health care systems, services, or suppliers for the purpose of increasing the likelihood of optimal clinical quality of care, measured by positive health outcomes for individuals and populations. An intervention could also be described as a strategy aimed at reducing the quality gap (the difference between health care processes or outcomes observed in practice and those potentially obtainable based on current evidence-based knowledge) for a group of patients representative of those encountered in routine practice. This review evaluates the effectiveness of QI interventions in reducing disparities in health and health care. Key questions include: Key Question 1. What evidence is available about the effectiveness of quality improvement strategies to reduce differences in health outcomes associated with selected disparities in patients with key conditions? Key Question 2. What evidence is available about the harms related to quality improvement strategies to reduce differences in health outcomes associated with selected disparities in patients with key conditions?