This article reviews the efforts of the Reagan Administration to mediate an agreement between Israel and Lebanon on the Israeli withdrawal, following its 1982 invasion of its northern neighbor. The USA, a superpower, was eventually successful in bridging the differences between the two disputants, whose contradicting interests are presented. Following procedural difficulties, the substantive points of contention were the nature of the security arrangements for Israel in southern Lebanon and the level of normalization between the two countries. The level of the American intervention in the talks gradually was raised to change the positions of the two sides and an agreement was reached only after the US Secretary of State engaged in shuttle diplomacy. A superpower is well suited for mediation. Yet, this article points out the limits on superpower leverage in pursuing its interests. The Israeli—Lebanese agreement was supposed to bring about a stronger central pro-Western Lebanese government. US mistakes, misperceptions and the domestic weakness of Lebanon were the reasons for the failure of this endeavor.