The scope of this study is narrow-the activities of a single ambas­ sador for little more than two years. The problem it treats is wide and universal-the origins of a great war. There can be no adequate history of the relations between states whieh does not take into account the knowledge, judgment and deci­ sions of individual statesmen. Diplomatie history, though only a part, is a necessary part of the history of international relations. Within a more or less c10sely circumscribed range of possibilities, men in power choose between alternative policies, with results they may or may not have anticipated. The historian therefore can and should describe the past, present and future, as it were, of the historical persons whom he studies: the past whieh provides them with oppor­ tunities and limitations, both objective and subjective; the present in whieh they act; the future in whieh the consequences of their actions appear, for the most part beyond their control. This is a study of the part played by a great diplomat-the perfect ambassador, his own age called hirn-in the formation of policy. My task has been a dual one. First, I have observed Arnauld de Pomponne at work. Second, I have attempted to evaluate the French plans for war against the Dutch republic, with particular attention to Pom­ ponne's contribution to them.