This article refers to debates explaining the end of the Cold War. It notes a variety of theoretical approaches but outlines two fundamental explanatory perspectives-the material and the ideational. The paper favours the ideational approach, and especially Gorbachev’s agency. Yet it underlines that the focus on agency does not automatically mean that an agent acted rationally and efficiently. The case of Gorbachev is a good illustration of partial reforms which were far from consistent. As a result, the article indicates a third, coincidental perspective which is necessary to an explanation of the end of the Cold War. It argues that elements of irrationality and coincidence cannot be ignored in the analysis of events accompanying the end of the bipolar rivalry. Finally, the paper formulates some conclusions about the rationality and predictability of contemporary international relations.