Since the end of World War II, nuclear weapons have fascinated humanity, providing a sense of security for many while also inspiring great fear. The first and only uses of nuclear weapons to date, against the Japanese cities of Hiroshima and Nagasaki in August 1945, were harbingers of a new and seemingly dangerous era. Although the influence of nuclear weapons on international politics is difficult to dispute, given the extremely limited actual use of these weapons, one could argue that their effect relied on perceptions or imagination of their power rather than on a body of experience associated with their actual use. Scholars could reasonably claim to have as much experience as the military in the field of nuclear warfare. The academic efforts examining the effects of nuclear weapons in international relations contributed to the development of specific fields of study that emerged in the Cold War, such as strategic studies, as well as direct contributions to policymaking in that era. There are many interrelated subtopics associated with nuclear weapons to consider. These include the development and use of nuclear weapons, their effects and related developments in terms of delivery mechanisms, concepts, major theorists, nuclear strategy, proliferation and efforts to counter it, the evolution of the arsenals held by various states, and the potential for and implication of nonstate actors developing nuclear capabilities. This article is limited to the two categories of nuclear weapons: those employing a fission reaction (atomic bombs, colloquially known as the A-bomb) and those employing a fission reaction in concert with a fusion reaction (thermonuclear weapons or hydrogen bombs, colloquially known as the H-bomb). Both of these are distinct from radiological devices that use a small explosion to spread nuclear material, and the latter is not discussed.