Improving the quality of health care has proven to be an elusive and difficult task. Health care organizations have experienced considerable difficulty in grasping all the individual-level, and system- level factors that shape quality. They have also been challenged to measure quality, to motivate providers to change their practices, and to implement quality improvement projects. The problems have been manifest in high rates of hospital readmission, high rate of preventable deaths and medical errors, uneven quality of care for people with inadequate insurance, and the introduction of new and expensive medical technologies without concomitant gains in life expectancy.