To understand why e-mail negotiations break down, we investigated two distinct elements of negotiators' relationships with each other: shared membership in a social group and mutual self-disclosure. In an experiment, some participants negotiated with a member of an outgroup (a student at a competitor university), whereas others negotiated with a member of an ingroup (a student at the same university). In addition, some negotiators exchanged personal information with their counterparts, whereas others did not. When neither common ingroup status nor a personalized relationship existed between negotiators, negotiations were more likely to end in impasse. These results are attributable to the positive influence of mutual self-disclosure and common group membership on negotiation processes and rapport between negotiators.