Since 1983, the Institute has helped resolve about 24 complex disputes. Intervenors in environmental cases have three essential characteristics: impartiality, a focus and expertise relating to process rather than subject matter, and the goal of achieving a mutually derived and acceptable outcome. There are, however, at least three different types of intervention processes: consensus building, mediation, and policy dialogues. These processes differ in their assumptions, intervenors' activities, and anticipated outcomes. The Institute suggests eight specific questions that must be answered before mediation begins. They consider representation, scope of the issue, deadlines, trust in the mediator, and commitment to a good faith effort to reach agreement. Contrary to popular opinion, mediation does not resolve basic differences, but allows parties to coexist despite their differences. It does not avoid conflict and is not nonadversarial. Other misconceptions are that mediation is an alternative to litigation and its success depends on negotiators liking and trusting one another. The Institute has found that mediators with expertise regarding the issues in a dispute may be less effective. The article discusses future directions in mediation and provides examples of cases mediated by Institute members. It includes six footnotes.