Institutional reform, or the review and restructure of state institutions, is broadly accepted as an element of transitional justice in both scholarship and practice. Nevertheless, discussion of institutional reform in transitional justice shows little consistency or coherence either in the institutions targeted for reform, nor in the objectives which institutional reform is said to pursue. The thesis identified conceptual confusion in the objectives attached to institutional reform in transitional justice, which move unsystematically between the pursuit of (1) past-focused accountability, (2) the prevention of reCUlTence of past crimes, (3) establishing the rule of law, and (4) the promotion and protection of human rights into the future. Moreover, the thesis identifies the unhelpful investment of institutional reform with transformative objectives by transitional justice scholars, without the elaboration of either the targeted institutions for refonn or meaningful indicators of transformation. The thesis responds to these identified shortcomings in the study and practice of institutional reform in transitional justice, firstly, by bringing greater conceptual clarity to the area and, secondly, and relatedly, by redressing the paucity of empirical data on institutional reform in transitional justice. To redress the pat1iality of underpinning data, and the need for greater clarity in what institutions to study, two large-N, cross-national qualitative databases were created on vetting and lustration processes and ombuds offices in transitional states. Furthermore, the thesis considers the application of depth and pervasiveness in institutional change theory to original empirical data of institutional reform in transitional justice. The thesis makes an original contribution to knowledge in two key ways. First, the thesis has developed a comprehensive and robust empirical data set on the scale of the practice of two case studies of institutional reform in transitional states. Second, utilizing this rich new data, the thesis works inductively to understand the diversity 0/ institutional reform in transitional justice and, drawing on institutional change theory, proposes a new framework for distinguishing between institutional reform and institutional transformation.