Papers that conceptualize ethnicity as an aspect of public health have increased in number over recent years in Social Science & Medicine, as elsewhere. This virtual special issue includes a selection of papers, mostly published in the last five years, to highlight recent developments in this area. The question of whether the risks associated with reifying ethnic categories in particular settings, thereby reinforcing racialised models of thinking, is addressed. The wisdom of seeking to construct ethnicity-type variables for the purpose of global cross-cultural comparison is queried.An unavoidable contradiction of studying ethnicity is the inevitable re-inscription of ethnic and racialised categories. Inequities in health outcome or quality of health service provision and uptake are injustices that have to be measured in order to be addressed. Whether research is qualitative or quantitative and whether or not an investigation finds inequalities, the definition of an ethnic group whether in terms of boundary or content, re-inscribes its existence as a cultural category. Furthermore, the familiar complexities of working with socio-demographic variables that relate to the individual and the population level, applies in the case of studying ethnicity and health.Ethnic groups exist because we behave as if they do: the social construction of ethnicity occurs as part of the definition of, and the search for, quantitatively and qualitatively significant differences between those groups. In appraising ethnicity, concomitant terms with over-lapping meanings are implied and, in the hope of avoiding terminological obfuscation, are briefly rehearsed below.