During the 1990s, the Israeli-Palestinian conflict underwent a profound transformation, which has proceeded slowly and sometimes with severe disruptions and retrogressions. This article examines the diverse contributions of different kinds of mediators to the transformation at various stages of the process. Particular attention is given to the Oslo negotiations, their forerunners, and subsequent negotiations. Comparisons are made regarding the different kinds of contributions made by different kinds of mediators. Mediators include intermediaries with leverage, such as a United States President, and mediators with few material resources, such as unofficial facilitators. At various stages of a conflict's escalation and de-escalation, different kinds of mediators can make appropriate and effective contributions. Making and building peace in protracted conflicts requires a wide variety of complementary actions by diverse actors, including persons within the adversary sides as well as by intermediaries. Mediating effectiveness is constrained by the circumstances of each adversary, the adversary relations, and the historical context.