This thesis analyzes the relationship between the themes of madness and immorality in two plays from William Shakespeare (Hamlet and Othello) and three stories from Edgar Allan Poe (“The Tell-Tale Heart,” “The Cask of Amontillado,” and “The Black Cat”). In the beginning, this thesis provides a brief overview of the history of madness, focusing on humanity’s longstanding association of mental illnesses with immorality. Afterward, an analysis of the aforementioned works reveals connections and differences in how the works portray the relationship between the two themes. Throughout the analysis, the thesis includes information regarding each author’s historical context (specifically in regard to social, cultural, and historical associations between madness and immorality) to explore the authors’ depictions of their mad characters. The plays Hamlet and Othello indicate that madness, on one hand, results from God’s bestowment of rightful punishment on those that pursue revenge against His prohibition of seeking revenge. The plays, although primarily Othello on this second point, also suggest that madness originates from the influence of diabolical sources that gain control over those that pursue immoral actions. On the other hand, Poe depicts the relationship between madness and immorality slightly differently. In the works of Poe, immorality and madness connect in that madness triggers immorality. In the end, this analysis reveals how these works, differing slightly in the details, nevertheless show humanity’s old, prevailing association between madness and immorality.