Hasidism (Hebrew: חסידות, romanized: Ḥăsīdūt) or Hasidic Judaism is a religious movement within Judaism that arose in the 18th century as a spiritual revival movement in contemporary Western Ukraine before spreading rapidly throughout Eastern Europe. Today, most of those affiliated with the movement, known as hassidim, reside in Israel and in the United States.
Israel Ben Eliezer, the "Baal Shem Tov", is regarded as its founding father, and his disciples developed and disseminated it. Present-day Hasidism is a sub-group within Haredi Judaism and is noted for its religious conservatism and social seclusion. Its members aim to adhere closely both to Orthodox Jewish practice – with the movement's own unique emphases – and the prewar lifestyle of Eastern European Jews. Many elements of the latter, including various special styles of dress and the use of the Yiddish language, are nowadays associated almost exclusively with Hasidism.