The chief purpose of this study is to develop a theoretical framework which can contribute to a broader theoretical understanding of the actions of the U.N. Security Council and its members. The framework rests upon a rationalistic foundation and it is set up with two different models of explanation; a first with focus on power and security and the second which is an institutional explanation. The framework is then applied on a case study in which the behavior of theUnited Statesand theUnited Kingdomin the Security Council are explained. The outcome of the paper is worth mentioning that the member nations have find the Security Council to be an important institution and that there is an apprehension of the precedential power of the institution. The study also points out that a permanent member is more likely to use its veto when there are strong national reasons of so doing. In general the developed theoretical framework seems to be well appropriate to explain states behavior in the Security Council and may provide a foundation for further theoretical studies on the subject.