The authors tested a motivated information-processing model of negotiation: To reach high joint outcomes, negotiators need a deep understanding of the task, which requires them to exchange information and to process new information. systematically. All this depends on social motivation, epistemic motivation (EM), and their interaction. Indeed, when EM (manipulated by holding negotiators process accountability or not) was high rather than low and prosocial rather than proself, negotiators recall more cooperative than competitive tactics (Experiment 1), had more trust, and reached higher joint outcomes (Experiment 2). Experiment 3 showed that under high EM, negotiators who received cooperative, rather than competitive, tactics reached higher joint outcomes because they engaged in more problem solving. Under low EM, negotiators made more concessions and reached low joint outcomes. Implications for negotiation theory and for future work in this area are discussed.