Henry Sidgwick's loss of religious faith is central to understanding the origins of the Cambridge school of welfare economics. The most prominent “public” manifestation of this loss and its impact on Sidgwick's thought was his Methods of Ethics, which was at once the capstone work of classical utilitarianism, cementing Sidgwick's place as one of the great philosophers of ethics during the Victorian period, and the source of his deep-seated need for the very religion to which he himself could no longer subscribe. Sidgwick's studies in political economy carried this ethical perspective into the economic realm, though the major impact came via his influence on A. C. Pigou, whose welfare analysis was very much a restatement of the Sidgwickian view, but undertaken with Marshallian analytical underpinnings. This article discusses Sidgwick's crisis of faith and his subsequent attempt to devise an ethical basis for social life that was divorced from religious concerns yet consistent with his own more general theistic stance. It also shows how the results of this search affected Sidgwick's work in economics and, ultimately, the Cambridge welfare tradition.