ONE of the more remarkable phenomena in the east European Jewish past was the triumph of hasidism, a mystical revival sparked during the mid-eighteenth century by the disciples of Israel Ba'al Shem Tov (the Besht, c. 1700–60). As those disciples began to buttress their master's doctrine of popular mysticism with palpable social and political power, they discovered that certain spiritual concepts could be expanded to accommodate and justify their roles as leaders in the mundane sphere. By the first decades of the nineteenth century, hasidism—now as much a sociopolitical innovation as a religious one—had emerged as a mass movement. It had won such overwhelming support that, in terms of sheer influence, hasidism deserves to be recognized as the most important phenomenon in modern east European Jewish history before the rise of the new Jewish politics at the end of the nineteenth century.

For all the scholarly attention dedicated to hasidism's origins, our understanding of its transformation into a thriving mass movement remains fragmentary and highly theoretical. While its origins have been well documented, hasidism as an emergent mass movement at the turn of the nineteenth century awaits comprehensive and systematic historical treatment. The scope of Moshe Rosman's groundbreaking and exhaustive look at the Besht and his circle within their historical context is limited to the lifetime of hasidism's founder alone.