Over the course of the conciliar years, progressive social movements arose in Dutch society. These were marked by the spread of youth culture and “flower power” as well as student demonstrations and the radicalization of trade unions. In the Catholic Church, this transformation was reflected in the emergence of grassroots communities and “critical parishes”. The examples considered here underscore their concerns: the modernization of liturgy, social critique and protest targeting the manner in which the Church operated, particularly in what concerned ecclesiastical celibacy and the obstacles put in the way of intercommunion between Catholics and Protestants. Widely covered in the media, particularly thanks to the efforts of the Septuagint, a group of protesting priests, the experience of the Dutch Catholic left was closely watched abroad in the late 1960s and early 1970s. It subsequently lost its social base and rapidly declined.