Prescriptive empiricism can be used to design international institutions in many fields, increasing their effectiveness in achieving their goals. This Article has argued that the goal of transitional justice, previously poorly conceptualized and undertheorized, should be to reconstruct social norms relating to mass violence. In order to be most effective at altering human behavior, the norms presented by transitional justice institutions must be internalized by local populations. This internalization requires that an affected society view the relevant accountability mechanism as legitimate. To attain this legitimacy, transitional justice mechanisms must be carefully tailored to meet the needs of particular societies recovering from mass violence. Much like democracy, a pluralist process will be messy and complex, but in return offers the promise of effectiveness—a bargain well worth the cost.