Osteoarthritis (OA), the most common form of arthritis, is a potentially devastating joint disease, affecting 27 million US adults. Its pathophysiology is marked by a gradual degenerative process accompanied by low-grade inflammation, and, although there is a strong correlation between age and OA risk, the abnormal changes that occur in the articular cartilage of people with OA differ notably from the typical changes associated with joint aging in several important ways. Risk factors for OA are multiple and span a variety of risk domains, such as lifestyle issues (eg, obesity and engagement in manual labor), genetic predisposition, sex and ethnicity (risk is higher in women and African Americans), and comorbidities. Clinical outcomes for people with OA typically involve pain, limitations of daily living activities, and overall diminution of quality of life (QOL). The need to evaluate the degree of this burden, as well as to determine treatment approaches and measure their success, requires instruments for measuring QOL. The 2 most commonly used instruments to measure QOL in OA are the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and the Medical Outcomes Study 36-Item Short-Form Health Survey. Both provide useful global information to the clinician and researcher alike about pain and function in patients with OA, although the WOMAC is more often used in the clinical setting as it is self-administered. A number of other pain and function-specific measures are also available that may provide additional insight into patient status when used in combination with global QOL instruments.