This chapter introduces the connections between procedural justice, substantive justice and legitimacy theory before considering the assessments of civil parties with regards to each in turn. It examines the extent to which the Extraordinary Chambers in the Courts of Cambodia (ECCC) is considered a legitimate institution in the eyes of civil parties, offering some tentative thoughts on the extent to which procedural justice might enhance perceived legitimacy and cushion negative outcomes within international(ised) criminal courts. The procedural justice literature frequently highlights the importance of interpersonal treatment to assessments of institutions. A number of procedural justice scholars have identified the quality of decision making as an important aspect of participants perceptions of procedural justice. The Substantive justice refers to the outcomes of the decision-making bodies and to the perceived fairness of the outcomes. The Judgements about an institution may be strongly influenced by interpersonal experiences, and how individuals feel they are treated in and by the institution.