Despite being inundated with publications on the subject historians today feel less confident than ever that they truly understand the Reformation. The prevalence of national paradigms, such as ‘confessionalisation’ in German Reformation studies and ‘revisionism’ in English Reformation studies, encourages scholars to focus their attention on local circumstances and on specific individuals in those localities without due attention to the bigger picture. The sheer volume of case-studies being generated risks the loss of an overall perspective, and threatens to obscure the magnitude and significance of the Reformation as a European phenomenon of the first order. It is critically important to appreciate the continental scale of the Reformation because it reflected the scale and severity of the crisis of authority that beset the Catholic Church during the half-century or so following Fr Martin Luther’s announcement of the sola scriptura principle. That crisis cannot be explained by reference to local circumstances only. It went to the very heart of the institution, and it posed an existential threat to the Catholic Church. Reformation historians have yet to explain convincingly why Luther’s challenge resonated with such devastating effects across the continent. This collection of essays reflects the impact of the Reformation across Europe and offers explanations of its impact.