Although negotiators need to build and sustain high-quality relationships, relatively little attention has been given to how they might accomplish this. Negotiation researchers have focused largely on the role of trust and trust violations in dealmaking, neglecting the insights that relationship science can offer. In this article, I integrate research from the close relationships and marriage therapy literatures with negotiation research. Based on this integration, I identify three common themes—relationship history, shared meaning, and relationship work—and draw out nine lessons for repair following actions that disrupt a relationship between negotiators. Drawing on these three themes and their associated lessons, I conclude by identifying four guiding principles for developing strong positive relationships. The first principle highlights the importance of acting within a critical window. Using the opening moments of a negotiation to establish positive emotional tone and cognitive interdependence builds a constructive foundation. Reappraising temporary impasses as transformational opportunities and resetting positive affect immediately after a temporary impasse stabilizes relationships and returns them to a positive trajectory. The second principle highlights the role of pauses. Stepping back from the moment of a temporary impasse enables negotiators to neutralize negative emotions, creating the psychological space to positively reappraise the impasse as a transformational opportunity. The third principle draws attention to the benefits of creating a positive skew within relationships, that is, increasing the salience of positive moments in a relationship’s history. Finally, the fourth principle draws upon the concept of positivity resonance to highlight the benefits of synchronicity: the alignment of cognitions and emotions in a way that establishes a shared perspective and a shared response to temporary impasses.