Achievement of medical and public health goals requires mutual understanding between professionals and the public, a challenge in diverse societies. Despite their massive diversity humans belong to one species, with race and ethnicity used to subgroup/classify humans and manage diversity. Classifications are contextual and vary by time, place and classifier. As classifications show major variations in health status, and risk factors, research using race and ethnicity has accelerated. Medical sciences, including epidemiology, are learning fast to extract value from such data. Among the debatable issues is the value of the relative risk versus absolute risk approaches (the latter is gaining ground), and how to assess ethnicity and race (self-assignment is favoured in the UK and North America, country of birth in continental Europe). Racial and ethnic variations in disease and risk factors are often large and usually unexplained. There is a compelling case for ethnic monitoring, despite its difficulties, for tackling inequalities and as a foundation for research. Medical and public health goals require good data collected in a racism-free social environment. Health professionals need to find the benefits of exploring differences while avoiding social division. Advances in health care, public health and medical science will follow.