The theory is advanced that Thomas Mann conceived of religion not as adherence to any orthodox dogma, but as an attitude defined as "religiously-based humanism," the characteristics of which are: scepticism toward both belief and disbelief; modesty; reverence for man despite a profoundly pessimistic view of human history; the belief that life is a process of atonement and purification, and that "higher health" is attainable only through the experience of death and "that which lies below"; and a sense of detachment from the mundane, everyday world. In Chapter I, Thomas Mann's religious ideas and Nietzsche's influence upon them are discussed in terms of Thomas Mann's major fictional works, his lectures, correspondence, and theoretical writings. Chapter II, an examination of religion in Buddenbrooks, attempts to show that the elements of Thomas Mann's conception of religion are already present in this first major work. In Chapter III the conclusion is drawn that Thomas Mann's "religiously-based humanism" had its origins in his early adulthood, and that throughout his life there was no fundamental deviation from this initial conception of religion.