The nonrandom distribution of ill health across and within populations is cause for ethical concern. Systematic differences in health across populations and subpopulations are a result of interactions among many types of influences operating on broad ecological, community, and individual levels. The operation of this web of influences potentiates health disadvantage for some populations and subpopulations and, conversely, enhances resilience to health threats in more advantaged populations. Understanding the genesis of inequity requires an appreciation of the dynamics of these interactions. Thus, research directed at elucidating the causes of inequity in order to facilitate policy changes requires the adoption of conceptual frameworks to guide more efficient and effective future scientific inquiry concerning this worldwide imperative.