 Race, ethnicity, and ancestry are three different concepts that can be used interchangeably in health research. There is no consensus on the definitions of these terms, leading to inconsistencies in research and a lack of clarity for researchers and readers. This paper examined the differences between these terms, assessed their reliability, and provided guidelines for using them in research. It was concluded that race, ethnicity, and ancestry should be treated separately in research, and that self-reporting should be preferred over observer-assigned classifications. This article was authored by Clara Lu, Rabiya Ahmed, Amel Lamry, and others.