Yiddish is a Germanic language spoken by Jewish people in many areas of the world, including Germany, Russia, Israel, the United States, Canada, Brazil, and Argentina. Originally a dialect of Middle High German, Yiddish developed among Ashkenazi Jews living in central and eastern Europe around the 10th century CE. The earliest known written document in Yiddish appears in a Hebrew prayer book from 1272. While Yiddish is a Germanic language related to German and English, it is written with the Hebrew alphabet rather than the Roman alphabet which used in other Germanic languages.

Yiddish contains influences from many languages besides German. Since the original Ashkenazi region included parts of France and bordered the Sephardic Jewish region in the Iberian Peninsula and southern France, there are some Romance language-based terms in Yiddish. Yiddish also contains many loanwords from Hebrew, often for terms relating to Jewish culture with no equivalent in Middle High German, such as the word for "synagogue." As the Ashkenazi culture spread into Eastern Europe, Slavic terms became incorporated into Yiddish as well. What were once the eastern dialects of Yiddish are the basis of nearly all forms of Yiddish spoken today.

Yiddish literature flourished in the 14th and 15th centuries and included songs and poems on both Jewish and European themes. The 14th century epic poem Dukus Horant is one of the most well known Yiddish works of this period. The development of the printing press led to an increase in the production of Yiddish works along with printed works in other languages. Yiddish retellings of biblical stories and Western epic works were popular during this era.

Many Ashkenazi women during the 16th century were literate in Yiddish, but not Hebrew. A significant amount of literary and religious works were produced by and for Jewish women. Glückel of Hameln was one of the most popular female writers in Yiddish, and her memoirs remain in print to the present day. The semi-cursive typeface most often used for works in Yiddish became known as vaybertaytsh, or "women's Yiddish," for this reason. Rashi is a different semi-cursive font used in rabbinical Yiddish commentary on religious texts, while the older square Hebrew letters are usually reserved for Aramaic and Hebrew language texts.

The late 19th and early 20th centuries, the same period in which secular Hebrew began to gain ground as a Jewish nationalist language, is considered the Golden Age of Yiddish literature. Important Yiddish plays, novels, and short stories date from this period. Three authors are mainly credited with the creation of the modern Yiddish literary genre: Sholem Yankev Abramovitch, Sholem Yakov Rabinovitsh, and Isaac Leib Peretz.

Yiddish suffered a serious blow during the Holocaust of the 1930s and 40s, when the European Jewish population was decimated. While millions survived, most Yiddish speakers became absorbed into other cultures and adopted their language. About a third of all Yiddish speakers today live in the United States. A handful of Yiddish newspapers and magazines have existed in the country, some still in print today. Isaac Bashevis Singer, a Polish-born Yiddish author living in the United States, won the Nobel Prize in literature in 1978.

Yiddish also boasts a significant speaking population in Israel, although its use there has been controversial since the foundation of the country. Many Zionists discouraged the use of Yiddish in the early days of the country, and state authorities heavily censored Yiddish works in the theater. Immigrants to Israel from Arab countries in which Yiddish did not exist contributed to the decline of Yiddish in Israel. While Hebrew remains the official language of the country, Yiddish also has a growing popularity among the younger population. Yiddish is the official language of the Jewish Autonomous Oblast in Russia, and it holds official minority language status in Sweden and Moldova.