This volume examines two major controversies that captured the theological attention of Andrew Fuller. In the wake of the Enlightenment, traditional Christian doctrine was challenged by various rationalistic and philosophical alternatives. A notable example is the thought of William Vidler, a former Baptist pastor who initially embraced Universalism and later Unitarianism. Vidler’s shift was influential enough that Fuller felt compelled to respond through a series of letters, later published in 1802. This critical edition, along with its introduction, provides an overview of Vidler’s theological position and Fuller’s rebuttal. This edition also includes Fuller’s debate with fellow Particular Baptist Abraham Booth, whom Fuller deeply respected. The conversation that developed between them contains some of Fuller’s most mature theological reflections on the doctrines of imputation, substitution, and particular redemption that impacted the transatlantic Baptist and evangelical world of the nineteenth century and have had ongoing reverberations up to the present day.