The present dissertation examines an identity-based third-party intervention as a means to alleviate competitive, conflict-laden intergroup negotiations. Although intergroup negotiations between opposing group representatives are likely to result in impasse and suboptimal outcomes, little is known about specific means to overcome these impairments. To address this shortcoming it is assumed that intergroup negotiations are resolved more effectively when they involve a mediator who promotes the construction of a common ingroup identity between opposing representatives. Five studies are reported examining the newly developed common-identity mediation" (CIM) intervention in a professional mediation context (Field Study; N = 117), in an integrative win-win negotiation (Experiment 1; N = 100), in a distributive zero sum context (Experiment 2; N = 160), and in competitive intergroup disputes (Experiments 3 & 4; N = 160; N = 190). In addition, the effectiveness of CIM is compared to two well-established dispute resolution procedures. The underlying mechanism accounting for the beneficial CIM effects is examined (Experiments 2-4), and a moderating boundary condition for its applicability is illustrated (Experiment 4). Implications for negotiations, dispute resolution, social identity research, and third-party intervention are discussed.