Most, it not all, negotiators would agree that trust is critically important in negotiations. But what is trust? How can trust be built? How can one accurately assess another’s trustworthiness? And can trust be repaired after a violation? These question, Donald Ferrin, Delun Tony Kong, and Kurt Dirks suggest, are as difficult to answer as they are important for negotiation effectiveness. Fortunately, trust researchers have made significant advances in the last 15 years toward answering these very questions. In this chapter, they summarize the empirical research on trust and discuss how it can be put into practice to effectively diagnose, build, and repair trust in the context of negotiations.