What lessons does the experience of transforming the security system in Sierra Leone have for security sector reform? This report from the Global Facilitation Network for Security Sector Reform and International Alert documents Sierra Leone’s security system transformation from 1997 to 2007. It chronicles the UK Government’s intervention, including its transition from direct implementer to adviser, and analyses key security issues that arose during the period. Sierra Leone’s experience shows how dedicated, capable people, given the space to reform their security institutions, can achieve a great deal under challenging circumstances. In 2007, Sierra Leone conducted a generally peaceful national election, which, given the levels of violence previously experienced in the country, reflected a remarkable change. From 1997 to 2007, Sierra Leone underwent a comprehensive transformation of the objectives of security provision and the mission, management and coordination of security. This transformation reached deep into and spread across a breadth of institutions, altering command structures, providing top-to-bottom training and establishing staff policies, procedures and behaviour.