Famed genealogist Henry Loius Gates Jr. uses traditional genealogical research (written records) and genetics (DNA testing) to discover the family history of well-known Americans. Genetic techniques include Y-chromosome DNA, mitochondrial DNA, and autosomal DNA analyses to infer both ancient and recent genetic relationships. The show's professionals typically spend hundreds of hours researching each guest. At the end, Gates gives the celebrity guest a "book of life" which contains all the information presented to them in that episode.