Negotiation has emerged as the foreign policy tool of choice within the broader context of “complex interdependence,” whether the issue is about human rights, economic development, and scientific, cultural, and educational exchanges, or organized crime, migration, disease, and pollution. The expanding role of international negotiation has been magnified by changes in the international system, including the emergence of issue-specific negotiation “subsystems,” regionalism, and international regimes. In addition to sovereign states, other actors involved in international negotiation and diplomacy include international governmental organizations/regional governmental organizations, nongovernmental organizations, multinational corporations, regional and substate actors, and even private individuals. A host of factors influence the behavior of these actors, such as cultural variables associated with national identity. Furthermore, both the character and the number of issues at stake in any particular negotiation play a crucial role in shaping the nature and complexity of the negotiation process. Research on diplomacy negotiation encompasses a substantial body of literature that provides a window into the complexity of the interactions that take place among and around diplomats. The intellectual richness of such literature offers a means of understanding the outcomes in the everyday world of diplomatic interactions, while also attesting to the value of pursuing multi-method approaches to social scientific research more generally.