This is a study of the religious-philosophy of spiritism and its manifestation as a social movement in Mexico at the turn of the twentieth century. It analyzes spiritism as a modern form of mysticism and as an ideology of social-political consequence. Chapters examine spiritist participation in debates of class and culture, the struggles between secular and religious authorities, shifting gender norms, and the growing opposition movement to the state under Porfirio Díaz. This dissertation argues that the spiritist movement generally reinforced and justified the trend of modernization for the few but that a minority of spiritists interpreted and applied the ideals of spiritual equality and transcendence towards the ends of social equality for women and the popular classes. While rooted in the Mexican setting, the work engages with transnational and comparative scholarship on esoteric religion and modernity, and addresses theoretical questions of wide interest to scholars of religion, social movements, science, medicine, the body, gender, and identity.