During the 16th and the 17th centuries the Mercedarian Order of friars, founded in the 1220s, underwent a period of reform from which it emerged utterly transformed. This study sets out to examine not only the context of that reform - the policies of the crown and the papacy, the condition of Catalonia and Spain at large, the circumstances prevailing within the Order and the dialogue with its past - but also to grasp the essence of monastic reform itself against this diverse background. The imposition of other than purely religious criteria onto the reform agenda alerts us to the deeper implications of monastic change in Early Modern Europe. For the Mercedarians the result by 1650 was a wholly new Order; the evolution of this process, by turns calculated and unexpected, is here explored.