The project will investigate what counts as responsible state conduct in relation to the possession of nuclear weapons. The rationale for this focus is the growing disjuncture in the contemporary global nuclear order between the nuclear possessor states on the one hand, and the vast majority of non-nuclear states on the other. The differences between these two groups of states has widened still further with the agreement of 122 states on 7 July 2017 to open for signature a Treaty banning the possession of nuclear weapons. None of the possessor states, or their allies, have signed or legitimized the ban process. Possessor states differ, however. Each state has its own history, context, and relationship to its nuclear arsenal. The project will focus on the conceptions of responsibility held by three very different nuclear weapon possessors: the United States, the United Kingdom, and North Korea.