International security studies (ISS) has significantly evolved from its founding core of “golden age” strategic studies. From the onset of the Cold War in the late 1940s through to the 1970s, strategic studies virtually was ISS, and remains a very large part of it. The fact that it continues to stand as the “mainstream” attacked by widening/deepening approaches further speaks to its status as a “core.” This core consists of those literatures whose principal concern is external military threats to the state, and the whole agenda of the use of force which arises from that. This core was originally focused on nuclear weapons and the military-political rivalry between the US and the Soviet Union, but has since adapted its focus to changes in the salience and nature of military threats caused by the end of the Cold War and 9/11. It includes literatures on deterrence, arms racing, arms control and disarmament, grand strategy, wars (and “new wars”), the use of force, nuclear proliferation, military technology, and terrorism. Debates within ISS are structured, either implicitly or explicitly, by five questions: (1) which referent object to adopt, (2) whether to understand security as internally or externally driven, (3) whether to limit it to the military sector or to expand it, (4) what fundamental thinking about (international) politics to adopt, and (5) which epistemology and methodology to choose.