Victims' registries are tools traditionally used in transitional justice processes to identify the population that has suffered human rights violations and to guide reparation programmes. Based on the experience of devising an official registry in Colombia, this paper analyses the conditions that make it a valid instrument for documenting human rights violations and for ensuring the recognition of victims. I argue that official registries are useful tools if they adopt appropriate elements (institutional design, the definition of victim, the methodology for analysis) from the outset and if they develop effective implementation. The political, legal, or administrative decisions that are adopted to resolve the challenges of the process have an impact on the utility of the registry as a tool for the recognition of victims and for the later implementation of reparation programmes.