As the world has become more interdependent, no state can stand alone against international terrorism without international cooperation. For international terrorist groups who seek mass casualties, WMD is an attractive option and can be regarded as a ‘low probability, high consequence’ problem. While the number of terrorist groups who would seek and use WMD is limited, those that are seeking them are intent on using them. Although all types of WMD are equally attractive to such terrorist, biological agents are the most cost effective and have many unique features that would appeal to a terrorist attacker. Intelligence on any terrorist group aspiring to WMD must be shared in a timely manner and NATO, along with other international organizations, has set up some initiatives to build cooperation and partnership in the control of proliferation of WMD.