This dissertation investigates the conviction amongst English orthodox Protestants, living between 1660 and 1730, that certain beliefs and actions were blasphemous. In a departure from the current historiography of blasphemy, it develops a cultural history of blasphemy as representation, exploring the nexus between conceptions and perceived manifestations of blasphemy in a theological context. By focusing on how contemporaries used the terminology of blasphemy in a diverse range of printed polemical literature, this dissertation re-evaluates a series of moral and doctrinal controversies by attending to the anxiety experienced by those who perceived fundamental threats to Christian truth and piety. The dissertation is divided into two parts: chapters on ungodly behaviour, swearing in particular, and attending the theatre consider supposed expressions of practical blasphemy; then chapters on antitrinitarianism, Quakerism, and the denial of Christ's miracles investigate representations of speculative blasphemy. I argue throughout that contemporary representations of blasphemy were commensurate with the theological conception of blasphemy as aggravated unbelief, the greatest sin which brought about an irrevocable breakdown in the relationship between a human being and God. My thesis reclaims a specific idea and language of blasphemy from the vague category and context of irreligion to provide new insights into the depth and breadth of contemporary fears about spiritual degeneracy and to help illuminate some of the most important theological controversies of the period.