Introduction The impact of transitional justice needs to be understood within the field’s broader objectives of contributing to societies that sustain peace and preventing the recurrence of violence. More specifically, the traditional aims of transitional justice have also included promoting the shift towards liberal democracy and the advancement of human rights institutions. However, as the field has expanded, transitional justice has sought to address new forms of conflict – at times applied even during conflict – with the consequence that intended impacts have also broadened to include promoting social cohesion, inter-communal reconciliation and addressing socioeconomic injustices and democratic consolidation. Within these more ambitious impact agendas, transitional justice has also expanded beyond a state-centred approach that functions through formal mechanisms such as truth commissions and trials to include a range of infor- mal non-state intervention such as traditional healing practices, participatory art, memorials and community reconciliation programmes. Each of these has its own goals and claims of impact. As such, transitional justice has become a global project that is in large part driven by international agencies, governments and foundations that seek to promote particular forms of transitional justice that contribute to a particular social change agenda. It is this agenda and an attempt to manage it more efficiently that often shape how impact is defined and how it is measured. Debates about impact are thus both political and technical in nature. Defining impact and impact assessment Social impact theory was formally articulated by Latane in 1981, looking to explain how change happens between groups and individuals through clustering, 13 ‘MEASURING’ TRANSITIONAL JUSTICE Impacts and outcomes Hugo van der Merwe, Richard Chelin and Masana Ndinga-Kanga DOI: 10.4324/9781315760568-13