Security sector reform (SSR) is a key concern in the current transformations which are sweeping across much of the Arab world. Given the crucial role security institutions have played in sustaining authoritarian regimes in the region, any transformation towards more democratic rule will necessarily also have to include a reform of these countries’ security sectors towards greater transparency, accountability and democratic control. This article explores the challenges and prospects of security sector reform in the first Arab country to have overthrown its autocratic leader, Tunisia. The main arguments advanced in this article are that the key SSR challenges in Tunisia since the fall of Ben Ali have been the reform of the country’s internal security apparatus and the judiciary, whereas military reforms are of limited importance. Even though in both of these areas actual reforms have been rather modest so far, and have focused more on purges rather than on structural transformations, Tunisia remains the most promising of all Arab countries which have toppled their long-standing leaders when it comes to achieving effective security sector reforms.