Miguel de Unamuno, perhaps the most influential author of modern Spain, wrote his Treatise on Love of God at the height of his career after suffering a crisis of religious faith. Like Saint Augustine's Confessions and much of Kierkegaard, the Treatise is a study of religious inwardness, and proposes to analyze how God can be found within as a beloved person. Not content with simple introspection, Unamuno also considers Church fathers like Athanasius, Origen, and Tertullian as well as modern religious scholars like Albrecht Ritschl, Auguste Sabatier, and Ernest Renan. Although Unamuno abandoned plans to publish the Treatise after Pope Pius X issued an encyclical against modernist theology, it deserves serious study as a prelude to his immensely successful Tragic Sense of Life and the concentrated work of a great thinker on a deeply serious subject.