In this dissertation I argue that the practice of penance has relevance beyond the church and in the political arena. To make my case, I build an ethic and then apply it to contemporary case studies. After situating penance in the context of Catholic tradition, I explore key resources of the penitential tradition which I use to build my ethic. I begin with the Irish monks of the fifth through ninth centuries who developed a robust system of penances which involved perpetrators in the process of seeing and undoing the damage of their sins. I then turn to Thomas Aquinas who understands penance as both a gift offered to sinners in the sacrament and a virtue which restores justice by capacitating sinners for right relationship. My final resource is Pope John Paul II whose jubilee gestures of repentance for the sins of Christians highlighted the communal dimension of penance. My final chapter brings these resources together into a single ethic. At the core of the ethic are what I construe as the three main practices in the performance of penance: lament, responsibility and repair. I show why these are distinct elements in a coordinated movement toward justice as the re-establishment of right relationship. As evidence, I examine the crisis of mass incarceration in the U.S. and suggest that construing punishment as penance would lead to more effective practice — and a convergence with ideas of the restorative justice movement. Second, I detail the challenges in Peru after a bloody internal armed conflict there, suggesting that insights from Aquinas in particular could help encourage perpetrators to participate in truth and reconciliation. Lastly, I suggest that communal practices of lament, within a penitential paradigm, can be a resource for the crises of moral wounds affecting U.S. soldiers returning from war.