Post-conflict societies struggle with several interlocking problems that often relate to security and legitimacy. To address these issues, the international community has often turned to Peacekeeping Operations (PKOs) or Security Sector Reform (SSR) programs. In this article, the authors present different aspects of these evolving concepts and what theoretical problems each tool aim to resolve. Furthermore, a symbiosis is found to exist between the ability of PKOs to provide protection in the immediate aftermath of conflict and the long-term benefits that SSR provides through the creation of accountable, efficient and professional security institutions. PKOs contribute to creating necessary preconditions successful SSR implementation, namely a safe environment. However, four additional preconditions must be met: a common vision, external support, local ownership and donor collaboration. Inability to provide these conditions will lead to a sub-optimal implementation and a security sector reform failing to deliver legitimate and professional institutions.