A morally contested political project has definitively entered late liberal international politics and human rights: material claims to reparatory justice for transatlantic slavery. In the absence of legal avenues with appropriate jurisdiction, claimants of redress for chattel slavery turn to an international network of political and legal forms of expertise. In anthropology and socio-legal research, studies on reparations have focused on transitional justice and redress initiatives within the framework of the nation-state. This project offers a monograph-length ethnographic study of formal reparations work across institutional scales and beyond the nation-state, showing the productive complexity of post-colonial rights-based claims for justice. Based on 18 months of qualitative research, the project explores transnational reparations work in three organizational contexts: the Office of the High Commissioner for Human Rights in Geneva, Switzerland, the Caribbean Community Secretariat and the Guyana Reparations Committee in Georgetown, Guyana. Regimes of Reparative Reasoning focuses on the legal-discursive political terrains that simultaneously enable and restrict the institutional circulation of reparation claims. Grounded in the belief that reparations are morally and materially imperative, this project argues: 1) formal reparations work is not principally a transformative political project but a liberal progressive project that speaks to established legal and political mechanisms; 2) to reckon with reparation claims for slavery and an emergent descent-based notion of legal personhood, we need to consider longer histories of dispossession: the beforelives of slavery. Ultimately, this study foregrounds the material multiplicity of reparation claims and how disparate national and organizational sites develop, exchange, and transform distinct forms of reparative reasoning.