On the basis of a social-functional approach to emotion, scholars have argued that expressing disappointment in negotiations communicates weakness, which may evoke exploitation. Yet, it is also argued that communicating disappointment serves as a call for help, which may elicit generous offers. Our goal was to resolve this apparent inconsistency. We develop the argument that communicating disappointment elicits generous offers when it evokes guilt in the target, but elicits low offers when it does not. In 4 experiments using both verbal (Experiments 1-3) and nonverbal (Experiment 4) emotion manipulations, we demonstrate that the interpersonal effects of disappointment depend on (a) the opponent's group membership and (b) the type of negotiation. When the expresser was an outgroup member and in representative negotiations (i.e., when disappointment did not evoke guilt), the weakness that disappointment communicated elicited lower offers. When the expresser was an ingroup member and in individual negotiations (i.e., when disappointment did evoke guilt), the weakness that disappointment communicated elicited generous offers from participants. Thus, in contrast to the common belief that weakness is a liability in negotiations, expressing disappointment can be effective under particular circumstances. We discuss implications for theorizing about the social functions of emotions.