This chapter develops a theoretical framework to understand the securitisation of Islamism in the post-9/11 world. It explores how the Global War on Terror (GWOT) transformed Islamism—both violent and non-violent—into a constructed security threat, legitimising extraordinary state measures in both Western and Muslim-majority countries. The chapter analyses how this framing enabled mass surveillance, political repression and civil rights restrictions, particularly targeting Muslim communities. It also examines how authoritarian regimes in the Muslim world, including Egypt and Saudi Arabia, appropriated counterterrorism rhetoric to suppress Islamist opposition. By highlighting the diversity of Islamist political actors—from democratic parties like Turkey’s AKP and Morocco’s PJD to extremist groups like Al-Qaeda and ISIL or ISIS—the chapter challenges reductionist narratives that equate all Islamism with violence. It argues that securitisation has obscured the pluralistic and evolving nature of political Islam, reinforcing authoritarianism and contributing to long-term instability.