Russian Jewish writer and folklorist best known for his play The Dybbuk.

Ansky was educated in a Ḥasidic environment and as a young man was attracted to the Jewish Enlightenment (Haskala) and to the populist doctrines of the Narodniki (Narodnik), a group of socialist revolutionaries. For a time he worked among the peasants and contributed articles to the Narodnik journal. His first novel, written in Yiddish, was published in 1884.

Compelled to leave Russia in 1892, he settled in Paris. Working as a factory hand, Ansky studied French folklore and socialist doctrine and became secretary to the revolutionary émigré Pyotr Lavrov. He also wrote articles and popular poems, many of them for the Jewish Workers' Party, the Bund. In 1905 he was permitted to return to St. Petersburg. He joined the Socialist Revolutionary Party, ideological heir of the Narodniki, and continued to write articles, folktales, and short stories on Jewish life.

In 1911 Ansky organized a large-scale ethnographic expedition to gather Jewish folklore, songs, melodies, manuscripts, and books. His fieldwork was interrupted by the outbreak of World War I, during which he did relief work and wrote about the destruction of the Jewish communities in Poland, Galicia, and Bukovina. Also during this period he produced his most famous work, the classic Yiddish drama Der Dibek (written 1914, first performed 1920; The Dybbuk). The play, which drew on Jewish mystical folklore, was widely translated and performed, most notably in the celebrated Moscow production of the Hebrew company Habima. It was also set to music and was filmed in Yiddish and Hebrew.

After the Russian Revolution Ansky was elected to the All-Russia Constituent Assembly, but in 1918 he left for Vilna. The following year he settled near Warsaw and devoted himself to preparing his collected works and to organizing a Jewish ethnographic society. His Yiddish works, in 15 volumes, were published between 1920 and 1925.