Ashkenazi Jews ( AHSH-kə-NAH-zee, ASH-; Hebrew: יְהוּדֵי אַשְׁכְּנַז, romanized: Yehudei Ashkenaz, lit. 'Jews of Germania'; Yiddish: אַשכּנזישע ייִדן, romanized: Ashkenazishe Yidn), also known as Ashkenazic Jews or Ashkenazim, are a Jewish diaspora population who were initially dispersed from their origins in the Levant by the Holy Roman Empire around the end of the first millennium CE. Their traditional diaspora language is Yiddish (a West Germanic language with Jewish and Slavic linguistic elements, which uses the Hebrew alphabet), which developed during the Middle Ages after they had moved from Germany and France into Northern Europe and Eastern Europe. For centuries, Ashkenazim in Europe used Hebrew only as a sacred language until the revival of Hebrew as a common language in 20th-century Israel.

Throughout their numerous centuries living in Europe, Ashkenazim have made many important contributions to its philosophy, scholarship, literature, art, music, and science.

The rabbinical term Ashkenazi refers to diaspora Jews who established communities along the Rhine in western Germany and northern France during the Middle Ages. Upon their arrival, they adapted traditions carried over from the Holy Land, Babylonia, and the western Mediterranean to their new European environment. The Ashkenazi religious rite developed in cities such as Mainz, Worms, and Troyes. The eminent rishon from medieval France, Rashi, has had a significant influence on the interpretations of Judaism by Ashkenazim.

In the late Middle Ages, due to widespread persecution, the majority of the Ashkenazi population steadily shifted eastward, moving out of the Holy Roman Empire into the areas that later became part of the Polish–Lithuanian Commonwealth; these areas today comprise parts of present-day Belarus, Estonia, Latvia, Lithuania, Moldova, Poland, Russia, Slovakia, and Ukraine.

Over the course of the late-18th and 19th centuries, those Jews who remained in or returned to historical German lands generated a cultural reorientation; under the influence of the Haskalah and the struggle for emancipation as well as the intellectual and cultural ferment in urban centres, they gradually abandoned the use of Yiddish and adopted German while developing new forms of Jewish religious life and cultural identity.

It is estimated that in the 11th century, Ashkenazim comprised 3 percent of the global Jewish population, while an estimate made in 1930 (near the population's peak) listed them as comprising 92 percent of the world's Jewish population. However, the Ashkenazi population was decimated shortly after as a result of the Holocaust that was carried out by Nazi Germany during World War II, which affected almost every Jewish European family. Immediately prior to the Holocaust, the worldwide Jewish population stood at approximately 16.7 million people. Statistical figures vary for the contemporary demography of Ashkenazi Jews, ranging from 10 million to 11.2 million. Israeli demographer and statistician Sergio D. Pergola, in a rough calculation of Sephardi Jews and Mizrahi Jews, implies that Ashkenazi Jews made up 65–70 percent of Jews worldwide in 2000. Other estimates place the Ashkenazim as comprising upwards of 75 percent of the global Jewish population.

Genetic studies on Ashkenazi Jews—researching both their paternal and maternal lineages as well as autosomal DNA—indicate that they are of mixed Levantine and European (mainly southern European) ancestry. These studies have arrived at diverging conclusions regarding both the degree and the sources of their European admixture, with some focusing on the extent of the European genetic origin observed in Ashkenazi maternal lineages, which is in contrast to the predominant Middle Eastern genetic origin observed in Ashkenazi paternal lineages.