This chapter examines the legal response to terrorism of a largely under-researched international organization, the Organization of Islamic Cooperation (OIC). After a brief introduction to the organization, the chapter examines relevant ‘soft’ and ‘hard’ law outputs. Though most of its outputs are technically ‘soft’ and therefore not formally binding, their potential significance, including normatively and politically, should not be underestimated. As the chapter reveals, some key outputs – such as regarding self-determination – seem to reflect influences of Islamic Shari’ah, some of which are eternal and immutable making them non-negotiable including in the context of ongoing negotiations on the UN Comprehensive Convention on Terrorism. Indeed, the OIC’s terrorism related soft law outputs are arguably more influential in practice than its weakly drafted and poorly ratified convention on terrorism. The chapter further reveals some concerning trends, notably an institutional move away from internationally agreed human rights principles underpinning international counter-terrorism efforts.