This book is a case study in the ongoing struggle of Christianity to define its relationship to modernity, examining representative Roman Catholic Modernists and anti-Modernists, exploring their relationship to their own historical context. Its aim is to counteract the tendency to lift the proposals made by the Modernists out of their setting and define them as a coherent, timeless philosophical/theological outlook, which should be avoided. The book seeks to correct the proclivity of some contemporary proponents of Modernist ideas to de-contextualize those ideas and recommend their endorsement without a critical reconsideration of historical changes. It sketches the nineteenth-century background of the Modernist crisis, identifying the problems that the church was facing at the beginning of the twentieth century; and offers a fresh perspective on the Modernist crisis, a perspective arising from the pioneering work undertaken by the Roman Catholic Modernism Working Group of the American Academy of Religion.