Book excerpt: George Williams' monumental The Radical Reformation has been an essential reference work for historians of early modern Europe, narrating in rich, interpretative detail the interconnected stories of radical groups operating at the margins of the mainline Reformation. In its scope--spanning all of Europe from Spain to Poland, from Denmark to Italy--and its erudition, The Radical Reformation is without peer. Now in paperback format, Williams' magnum opus should be considered for any university-level course on the Reformation.