The Hasidic movement started in the 1700's (CE) in Eastern Europe in response to a void felt by many average observant Jews of the day. The founder of Hasidism, Rabbi Israel Baal Shem Tov (referred to as the "Besht," an acronym of his name) was a great scholar and mystic, devoted to both the revealed, outer aspect, and hidden, inner aspect of Torah. He and his followers, without veering from a commitment to Torah, created a way of Jewish life that emphasized the ability of all Jews to grow closer to Gd via everything that we do, say, and think. In contrast to the somewhat intellectual style of the mainstream Jewish leaders of his day and their emphasis on the primacy of Torah study, the Besht emphasized a constant focus on attachment to Gd and Torah no matter what one is involved with.
Early on, a schism developed between the Hasidic and nonHasidic (i.e., Misnagdim, lit. "opponents") Jewish movements, primarily over real or imagined issues of halachic observance. The opposition was based on concern that the Hasidim were neglecting the laws regarding appropriate times for prayer, and perhaps concern about the exuberance of Hasidic worship, or a concern that it might be an offshoot of false messiahs Shabbtai Zvi or Jacob Frank. Within a generation or two, the rift was closed. Since then, many Hasidic practices have influenced the Misnagdim, while the Misnagdim, in turn, moderated some of the extremes of early Hasidism. Nevertheless, the dispute between particular groups of Hasidim and Misnagdim continues to this day, especially in Israel.
Today, Hasidim are differentiated from other Orthodox Jews by their devotion to a dynastic leader (referred to as a "Rebbe"), their wearing of distinctive clothing and a greater than average study of the inner aspects of Torah.
There are perhaps a dozen major Hasidic movements today, the largest of which (with perhaps 100,000 followers) is the Lubavitch group headquartered in Brooklyn, NY. Other groups include the Bobov, Bostoner, Belzer, Gerer, Satmar, Vizhnitz, Breslov, Puppa, Bianer, Munkacz, and Rimnitz. In Israel, the major Hasidic groups besides the Lubavitch include: Gor (Gerer), Viznitz and Bealz (Belzer).