The Ashkenazim are awell-studied populationwith a dynamic and unique history. The spread of Jew- ish populations from the Middle East to locations in the Diaspora in the past 2000 years repre- sents a microcosm of the evolutionary processes affecting modern humans as they dispersed out of Africa (e.g. founder effects, migrations, admix- ture and adaptation). Ashkenazim – Jews who trace their ancestry to founders who moved to the Rhine Valley in the fourth century – are no exception. Recent studies both support and refute long-standing hypotheses of Ashkenazi origins. Together, the results Strengthen the inferences that Ashkenazi Jews trace their ancestry to a genet- ically diverse population in the Middle East that underwent a series of founder events – reducing genetic diversity relative to the ancestral population – and that subsequently experienced significant gene flow during the period of Ashkenazi residency in Europe.