The term "Ashkenazi" refers to Jewish settlers who established communities along the Rhine River in Western Germany and in Northern France dating to the Middle Ages. Once there, they adapted traditions carried from Babylon, The Holy Land, and the Western Mediterranean to their new environment. The Ashkenazi religious rite developed in cities such as Mainz, Worms, and Troyes. The eminent French Rishon Rabbi Shlomo Itzhaki (Rashi) would have a significant influence on the Jewish religion.
In the late Middle Ages, due to religious persecution, the majority of the Ashkenazi population shifted steadily eastward, moving out of the Holy Roman Empire into the areas later part of the Polish-Lithuanian Commonwealth (comprising parts of present-day Belarus, Latvia, Lithuania, Moldova, Poland, Russia, and Ukraine). In the course of the late 18th and 19th centuries, those Jews who remained in or returned to the 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 centers, they gradually abandoned the use of Yiddish and adopted German, while developing new forms of Jewish religious life and cultural identity.
The Holocaust of the Second World War decimated the Ashkenazim, affecting almost every Jewish family. It is estimated that in the 11th century Ashkenazi Jews composed three percent of the world's total Jewish population, while an estimate made in 1930 (near the population's peak) had them as 92 percent of the world's Jews. Immediately prior to the Holocaust, the number of Jews in the world stood at approximately 16.7 million. Statistical figures vary for the contemporary demography of Ashkenazi Jews, ranging from 10 million to 11.2 million.Sergio Della Pergola in a rough calculation of Sephardic and Mizrahi Jews, implies that Ashkenazi Jews make up less than 74% of Jews worldwide. Other estimates place Ashkenazi Jews as making up about 75% of Jews worldwide.
Genetic studies on Ashkenazim—researching both their paternal and maternal lineages—suggest a predominant amount of shared Middle Eastern ancestry, complemented by varying percentages of European admixture. These studies have arrived at diverging conclusions regarding both the degree and the sources of their European ancestry, and have generally focused on the extent of the European genetic origin observed in Ashkenazi maternal lineages. Ashkenazi Jews are popularly contrasted with Sephardi Jews (also called Sephardim), who descend from Jews who settled in the Iberian Peninsula, and Mizrahi Jews, who descend from Jews who remained in the Middle East.
Sometime in the early medieval period, the Jews of central and eastern Europe came to be called by this term. Conforming to the custom of designating areas of Jewish settlement with biblical names, Spain was denominated Sefarad (Obadiah 20), France was called Tsarefat (1 Kings 17:9), and Bohemia was called the Land of Canaan.
By the high medieval period, Talmudic commentators like Rashi began to use Ashkenaz/Eretz Ashkenaz to designate Germany, earlier known as Loter, where, especially in the Rhineland communities of Speyer, Worms and Mainz, the most important Jewish communities arose. Rashi uses leshon Ashkenaz (Ashkenazi language) to describe German speech, and Byzantium and Syrian Jewish letters referred to the Crusaders as Ashkenazim. Given the close links between the Jewish communities of France and Germany following the Carolingian unification, the term Ashkenazi came to refer to both the Jews of medieval Germany and France.