Hasidism, sometimes Hasidic Judaism, (Hebrew: חסידות, hasidut, Ashkenazi pronunciation : [χaˈsidus]; originally, "piety") is a Jewish religious sect. It arose as a spiritual revival movement in contemporary Western Ukraine during the 18th century and spread rapidly through Eastern Europe. Today most affiliates reside in the United States, Israel, and Britain. Israel Ben Eliezer, the "Baal Shem Tov", is regarded as its founding father, and his disciples developed and disseminated it. Current Hasidism is a sub-group within Ultra-Orthodox ("Haredi") Judaism and is noted for its religious conservatism and social seclusion.
Hasidic thought draws heavily on Lurianic Kabbalah and to an extent is a popularization of it. Teachings emphasize God's immanence in the universe, the need to cleave and be one with Him at all times, the devotional aspect of religious practice, and the spiritual dimension of corporeality and mundane acts. Hasidim, the adherents of Hasidism, are organized in independent sects known as "courts" or dynasties, each headed by its own hereditary leader, a Rebbe. Reverence and submission to the Rebbe are key tenets, as he is considered a spiritual authority with whom the follower must bond to gain closeness to God. The various "courts" share basic convictions but operate apart and possess unique traits and customs. Affiliation is often retained in families for generations, and being Hasidic is as much a sociological factor, entailing birth into a specific community and allegiance to a dynasty of Rebbes, as it is a purely religious one. There are several "courts" with many thousands of member households each, and dozens of smaller ones.