What was existentialism? At its heart, Noreen Khawaja argues, existentialism was an effort to translate Protestant piety into a secular philosophy. While there have been many attempts to define existentialism from within as a coherent philosophical program and even as a movement, Khawaja s book is the first study of existentialism from the standpoint of intellectual history and the first to look systematically at the role that Christianity played in the development of existential thought. Focusing on Soren Kierkegaard, Martin Heidegger, and Jean-Paul Sartre, Khawaja illuminates the key moments in existentialism s reconstruction of Protestant piety within the confines of secular philosophy. Heidegger once described his work as an exercise in the piety of thinking. Khawaja s book shows the historical and systematic truth behind this metaphor. Notwithstanding Heidegger, thinking has not always been a pious act. But for a certain group of European intellectuals in the late-nineteenth and twentieth centuries, it became so. "The Religion of Existence "will appeal to scholars of modern Christianity, philosophers, and historians of European philosophy, as well as those engaged with the theoretical and historical problems of secular and post-secular modernity. "