Since the end of the Cold War, security sector reform (SSR) has emerged as a key part of the development and state building agendas in post-conflict nations. While this is incrediblyimportant, it is also incredibly expensive. Most modern research on the issue focuses on how to integrate SSR into a political process, treating fiscal sustainability as secondary. However, this thesis suggests a change in paradigm from thinking of political and fiscal sustainability in SSR as mutually exclusive to one that thinks of them as mutually reinforcing. This conclusion is reached in two ways. First, a qualitative analysis finds that fiscal sustainability is key to political sustainability, and that failing to consider fiscal sustainability can have significant consequences that undermine the political goals of the process originally set out. Second, this thesis builds on the first conclusion by presenting a quantitative, politically grounded model that allows policy makers to see the fiscal consequences of political choices. This model the first tool to operationalize fiscal sustainability in a way that provides flexibility for adapting tovolatile political environments. Because it is intended to be used by those in the policy making process, the model is applied to the Somali context to show its function. This reveals a number of consequences and conclusions for the Somali political process that would not be possible without the consideration of fiscal sustainability and use of the model. In the end, the analysis here not only shows why fiscal sustainability is important in SSR, but how it can be integrated into the process, thereby facilitating a change the way SSR is approached by policy makers and academics alike.