For many decades, the Middle East security sector (MESS) has played a significant, and sometimes a dominant, role in the politics, society, economy and culture in many of the region’ states. This chapter presents a conceptual framework for studying the MESS and its main roles and suggests ways to implement it focusing on three main areas where these roles are manifested: First, the process of state formation, broadly defined; second, the state’s pattern of civil-security relations, where the MESS and informal actors (“security networks” and “deep states”) operate; third, the relationship between the MESS and inter-communal relations in divided societies.