Ample evidence suggests that mediators increase the probability of agreements and that mediated agreements are more stable than un-mediated ones. Further research describes how agreements' content is crucial for lasting peace. However, we lack a theory explaining why conflict parties agree on specific content in the first place and how mediators influence agreement content. We propose a framework of negotiation processes and highlight how mediators shape their content. We argue that two factors define negotiation processes: the difficulty of issues on the table and the willingness and ability to compromise among the negotiating parties at the table. Existing scholarship outlines that, e.g., bargaining problems hamper compromise and proposes that mediators may increase actors' overall willingness or ability to make concessions by facilitating information flow and mitigating commitment problems. We suggest mediators have further, more nuanced means to foster meaningful agreements. We deduce three patterns of how mediators promote or deprioritize content and foster agreements on challenging issues. Our theoretical framework translates directly into a statistical model, allowing us to test the predicted patterns using data on peace agreements in intrastate conflicts between 1990 and 2012. As expected, we find that mediators successfully promote compromise on the most difficult content. Moreover, mediators appear to deprioritize less controversial topics. The analysis highlights how mediators may alter and potentially improve agreement content, even when they cannot increase belligerents' overall willingness or ability to compromise. Beyond armed conflict studies, our framework may inform research on third party influence in negotiations over specific content.