Data from the 2000 census reveal that the United States is becoming increasingly diverse at a rapid pace. Between 1990 and 2000, the Latino/Hispanic population increased by >50% (Guzmán, 2001), and the Black and Asian populations both increased at faster rates than the total population (Barnes & Bennett, 2002; McKinnon, 2001). Population projections indicate that between 2000 and 2010, the proportion of individuals considered ''White alone (not Hispanic),'' will decrease from 69.4% to 65.1%, and by 2050 will be barely a majority, at 50.1% of the total population (US Census Bureau, 2004). The increasing diversification of the population creates certain responsibilities for the execution of ethical science. Guidelines for federal funding require documentation of efforts toward appropriate representation of racial and ethnic minorities within study design. In our own field, submission guidelines for the Journal of Pediatric Psychology indicate that articles must specify the racial/ethnic composition of study samples, and questionnaires, interviews, and procedures that are used with diverse samples must have appropriate normative data. At a minimum, when study samples lack diversity, issues of generalizability and applicability to diverse samples must be addressed within every manuscript. There is also, however, an increasing need for research that specifically assesses the complex relations among race/ethnicity, culture, and health outcomes. The purpose of the Journal of Pediatric Psychology's special section on diversity and health care disparities is to facilitate the presentation of research that addresses (a) the interface between culture and illness management behavior, (b) the mechanisms of underlying health care disparities, and (c) the complex relations among socioeconomic status, racial/ethnic background, and disease outcomes.