This chapter describes the earliest stirrings of religious dissent in the Low Countries during the period 1520–1540. Reformist ideas coming out of the Holy Roman Empire and Swiss cities, especially the protests of Luther and Zwingli, followed continental trade routes to circulate in the Netherlands by 1520. Combined with long-standing humanist criticisms of the church, these reform ideas quickly gained a small but significant audience among the urban, literate populations of the region, first among clergy and intellectuals and then among the broader middling sort. By the mid-1520s a vocal minority was espousing religious ideas the Catholic Church deemed heretical. By the 1530s an even more radical evangelical movement, Melchiorite Anabaptism, found a broad following, especially in the northern provinces. This radicalism climaxed in 1535 with the Anabaptist kingdom of Muenster and Anabaptist attempts to overthrow the government of Amsterdam. By this time Charles V had instituted a new judicial apparatus of laws and courts to suppress heresy. This judicial regime proved at least temporarily successful in staunching the spread of heresy in the region after the Muenster debacle.