This paper examines the effect of negotiators' expectations of their opponents' competitiveness on negotiators' predictions of their own behavior, their actual behaviors, and their negotiated outcomes. Study 1 examined negotiators' predictions of how they would react when faced with a very competitive versus a not competitive opponent and found that negotiators believed they would become more competitive, less cooperative, and less likely to make concessions when negotiating with a very competitive opponent. Studies 2 and 3 examined actual behaviors during a negotiation and found that negotiators who expected very competitive opponents actually became less competitive, as evidenced by setting lower, less aggressive reservation prices and agreeing to lower negotiated outcomes. Study 3 further revealed that own reservation price mediated the relationship between competitive expectations and negotiated outcomes. Finally, Study 4 examined more naturally occurring expectations in a negotiation and found that expectations of greater competitiveness were associated with lower negotiated outcomes.