The Fissile Material Cut-Off Treaty (FMCT) is an envisaged treaty on nuclear non-proliferation and, possibly, disarmament. If negotiated, the FMCT will provide a legal ban on the production of fissile material for weapons purposes and, perhaps, codify substantial reductions in the existing stockpiles of such material. However, so far the FMCT has not been negotiated. The purpose of this thesis is to explore why this is so by examining the hypothesis that if states are either unwilling or incapable of paying the costs of enforcement, they will avoid negotiating so called "deep" agreements. Arguably, the FMCT is a "deep" agreement. The analytical strategy chosen is a “pattern- matching” strategy where we operationalize the variables of the hypothesis (unwillingness and incapacity) and compare this theoretical decision pattern with the actual policies of two potential FMCT member states: the United States and Pakistan.The analysis showed that, concerning the United States, the predicted decision pattern fit quite well with Washington’s policies, indicating that the United States is concerned about non-compliance and about the costs of verification and enforcement, and that this may to some extent explain why it is reluctant to the FMCT. However, the main reason is that full participation is currently not deemed likely, and would require concessions which the United States is currently not willing to give.As for Pakistan, the analysis showed that to some extent the policies of Islamabad also coincide with the predicted decision pattern. In other words, that Pakistan also is concerned about non-compliance and about the costs of verification and enforcement, and this could lead them to avoid the FMCT in the future. At present, however, Pakistan is evidently not ready to commit itself to an FMCT as it still feels the need to produce fissile material. Further, India’s strengthened position in the region, helped by the U.S.–India Strategic Partnership, is of greater concern to Pakistan than anything else at the moment.In conclusion, the hypothesis of Downs et al. does offer a valid explanation to the FMCT stalemate, at least when it comes to the policies of the United States and Pakistan. While the analysis has shown that the case of the United States fits the predicted decision making pattern slightly better than the case of Pakistan, neither of the two countries seem particularly interested in advancing FMCT negotiations at present. Both countries seem to have concerns about non-compliance as well as the costs of verification and enforcement, and neither believes that full participation is likely.