When faced with interpersonal transgressions, some victims maintain unforgiveness towards their offenders. Researchers have identified emotions and cognitions experienced by victims who maintain unforgiveness, but the literature has yet to move beyond investigating the intrapersonal experience of unforgiveness. In my dissertation, I investigated the interpersonal communication of unforgiveness from victims to offenders. In Chapter 2, I conducted 40 interviews with community members and university students to identify the strategies through which unforgiveness is communicated. I also probed into perceptions of the effectiveness and appropriateness of the strategies. The findings suggest that there are eight strategies that victims use to communicate their unforgiveness, and these strategies were mostly seen as effective and appropriate by victims and offenders. In Chapter 3, I developed the Communicating Unforgiveness Scale (the CUFS) to measure the strategies for communicating unforgiveness identified in Chapter 2. Undergraduate students (N=498) completed the CUFS and other measures (e.g., an existing scale that measures the communication of forgiveness) that I used to validate the CUFS. An Exploratory Factor Analysis (EFA) on the items on the CUFS suggested that unforgiveness is communicated using five strategies. I found evidence for the convergent and discriminant validity of the CUFS. In Chapter 4, I recruited participants from the University of Calgary, PROLIFIC, and social media (N=235). I started by conducting a Confirmatory Factor Analysis (CFA) to corroborate the findings of the EFA in Chapter 3. I found that unforgiveness is communicated using the same five strategies identified in Chapter 3. Next, I conducted three path analyses to test whether the strategies for communicating unforgiveness mediate the associations between unforgiveness and psychological/relational outcomes. Overall, the findings support partial mediation. This dissertation includes the first set of empirical studies that investigate the communication of unforgiveness. The findings make several important contributions: theoretical (e.g., identifying strategies for communicating unforgiveness which extends the current understanding of unforgiveness beyond intrapersonal experiences); methodological (e.g., introducing a scale for measuring the communication of unforgiveness); and practical (e.g., helping individuals and clinicians understand the psychological and relational correlates of the different strategies for communicating unforgiveness).