This dissertation argues that eighteenth-century authors, in writing sequels to their own works, raise important questions about narrative closure, ideal justice, and the literary canon. It considers works by both traditionally canonical writers (e.g., Daniel Defoe's Farther Adventures and Serious Reflections and Samuel Richardson's Pamela II) and less familiar authors (e.g., Sarah Fielding's Familiar Letters and Volume the Last and Frances Sheridan's Conclusion of the Memoirs of Miss Sidney Bidulph). Sequels demand a re-examination of how we theorize novelistic form and closure (as found in such works as Henry James's The Art of Fiction and Frank Kermode's The Sense of an Ending). Sequels do not conform to classical (i.e., Aristotelian) theories of artistic closure, which treat an artistic production as a complete work composed of 'a beginning, a middle, and an end' with a uniform effect on a spectator. Sequel-writers often devote more attention to perspectives that may be excluded from their earlier novels, consequently complicating earlier assessments of a character's moral worth or revealing the impermanence of a 'happy ending.' Sequels are thus frequently at odds with the dramatic convention of 'poetic justice' and often introduce a competing aesthetic, 'poetic mercy.' The presence of the sequel calls for a reformulation of the literary canon: without attentiveness to sequels, critics ignore the 'story' as many earlier audiences have read it and risk misrepresenting how authors engage with their subject matter. The literary sequel complicates our understanding of the eighteenth-century novel and enables us to engage with questions of justice and literary endings in a different way.