In this paper we draw on our work at the World Bank to provide practical guidance on how the Bank and other donors might operationalize the WDR 2011 so as to promote the emergence of legitimate and effective institutions to manage justice and security in fragile and conflict affected states (FCS). Our approach reflects three propositions about how justice and security institutions develop and how donors can engage. First, we understand that justice and security are not merely the remit of particular forms of institution, but rather represent core functions of all public authorities. Tis requires a broader view of the arenas and entry points through which development policy and programming may impact on justice and security. Second, engagements to support legitimate and effective justice and security institutions requires looking beyond the laws, procedures, skills and technologies that are the usual focus of development programs, to the processes of elite bargaining, collective struggle and normative change that shape institutions over time. Third, the impacts of development interventions on these processes extend far beyond the typically narrow remit of technical “capacity-building”. Understanding these implications — intended or not — requires a closer review of social and political change in particular contexts.