Ashkenazi Jews are a Jewish diaspora population that formed in the Holy Roman Empire around the end of the first millennium CE. They traditionally speak Yiddish, since their migration to northern and eastern Europe in the late Middle Ages due to persecution. The term "Ashkenazi" became identified primarily with German customs and descendants of German Jews. Although strictly speaking, “Ashkenazim” refers to Jews of Germany, the term has come to refer more broadly to Jews from Central and Eastern Europe.

In an ethnic sense, an Ashkenazi Jew is one whose ancestry can be traced to the Jews who settled in Central Europe. For roughly a thousand years, Ashkenazi Jews were a reproductively isolated population in Europe, despite living in many countries, with little inflow or outflow from migration, conversion, or intermarriage with other groups, including other Jews.

Today, about half of Jewish people around the world identify as Ashkenazi, meaning that they descend from Jews who lived in Central or Eastern Europe. The modern religious denominations developed in Ashkenazic countries, and therefore most North American synagogues use the Ashkenazic liturgy.