Truth commissions aim to promote transparency, accountability, and reconciliation by compiling detailed narratives of political violence. To achieve this end, both victims and perpetrators of abuses must testify. Yet, little is known about how commissions can be designed to facilitate perpetrator testimony. This article develops a theory of perpetrator participation in truth commissions, with a focus on institutional design. The article then evaluates the effectiveness of four design features—amnesties, subpoena powers, dual-party agreements, and spiritual frameworks—in facilitating perpetrator testimony in the truth commissions in Sierra Leone, South Africa, and Timor-Leste. The analysis indicates that the theoretical constructs developed are present, functional, and influential for perpetrator participation in the three commissions. And, while no individual design feature is essential, the case studies reveal that perpetrator participation may not be forthcoming without a robust dual-party agreement and/or a resonant spiritual framework. This underscores the importance of normative foundations for perpetrators’ engagement with commissions. Crucially, though advantageous features may be present, the criteria required for them to function may not be met, resulting in no effect or a negative effect on participation.