This entry defines the term disparity as measurable differences between groups on a number of indices. The term disparity originated in France in the 16th century and has been used as a barometer of progress in social justice and equality in the United States. When disparity is examined across the U.S. population over a longitudinal period, it is clear that disparities continue to exist and that they distinguish groups by race, income, class, and gender. African American and Native American populations have historically ranked higher in prevalence and incidence than other populations on most indices of disparity. However, the level of adverse health and social conditions has declined for all population groups in the United States. The disparity indices include mortality rates, poor health, disease, absence of health insurance, accidents, and poverty. Max Weber’s theory of community formation is used in this entry to explain the continued presence and distribution of disparities. Other theoretical frameworks are utilized to buttress the major hypothesis by Weber that social ills tend to result from structural faults rather than individual choice. Social workers are seen as being in a position to challenge the structural origins of disparities as part of their professional commitment to social justice.