This dissertation aims, first, at accounting for the timing of implementation of Transitional Justice (TJ) policies and, second, at comparing TJ trajectories and outcomes in countries that had negotiated transitions from authoritarianism to democracy. Specifically, it focuses on TJ mechanisms adopted long after the transition to democratic rule and asks why now? Furthermore, it explores why states with the same type of transition differed in their TJ trajectories later on, comparing a case of ‘robust’ implementation (Uruguay), a case where only ‘victim-centered’ measures were approved (Spain), and a case that sits in between (Brazil). Combining an agentic approach with a path-dependence theoretical framework, it argues that both supply and demand-side factors matter in understanding the timing of implementation of TJ policies and the type of policy adopted, but that the historical-normative context for dealing with the past in each country – their ‘mnemonic regime’ – sets different boundaries in each case. Zooming in into seven cases of ‘late’ TJ policy implementation and looking at the supply and demand factors at play, it concludes that political opportunities for TJ measures arise when the combination between the preferences of the executive and the levels of external pressure outweigh or match the perceived costs of specific measures. In other words, both (1) agendasetting pressures and (2) a (usually left-wing) government sympathetic toward TJ measures are necessary, but the choice of policy instrument depends on how strong preferences, pressures, and perceived costs are. Differences in these dimensions are, in turn, not independent from the ‘mnemonic regime’ actors have been embedded in, with the historical experience of Uruguay contrasting with the one of Spain and Brazil in the extent to which the political crimes of the dictatorship have been an object of social and political contention over the years. In Spain and Brazil, instead, the ‘reconciliation ethos’ of the transition complicates the enactment of (robust) TJ policies. Crosscountry differences in ‘mnemonic regimes’ and TJ outcomes are, in turn, also explained by structural differences related to (1) pre-authoritarian democratic experiences, (2) repression’s characteristics, (3) correlation of political forces at the transition stage and (4) international influences.