Since the early 1990s, security considerations have increasingly been used to justify foreign economic aid. While aid is rarely used to directly finance security and defense budgets, it frees up governments to spend more on security and less on domestic programs. This is a fact that cannot be disregarded. According to 2004 figures, 16% of international aid contributed to an increase in military spending. What are the key conditions for a successful security reform program in fragile states? This paper attempts to provide answers by drawing on debates in the international community and relying on several examples of past interventions.