Occasionally, analytic models have found their way into complex policy negotiations. This article scrutinizes four such cases. When they appear independent and credible, models can play a variety of traditional mediating roles: They can foster learning, help define the negotiating agenda, stimulate communication, and suggest joint gains. These constructs can also offer artificial common ground for proposals to be tested, disputants' differences to be dovetailed, and adversaries “convinced” to move from entrenched positions without “conceding” to bargaining opponents. Yet, where the negotiators' basic values or ideologies actively clash, the special kind of rationality provided by models may prove to be irrelevant.