Think tanks, as intermediaries between specialized knowledge and decision-making structures, play an increasingly significant role in the processes of diplomacy and foreign policy. However, the degree of their influence on diplomacy depends on institutional structure, level of independence, resources, communication (media) networks, and their ability to access decision-making processes and diplomatic negotiations. Adopting an institutionalist approach, this research conducts a comparative analysis of the performance and operational influence of four selected think tanks, Brookings and Carnegie (US) versus Sharif Governance Institute and the Center for Political and International Studies of the Ministry of Foreign Affairs, on diplomacy through media. The qualitative methodology uses comparative case studies, document analysis, examination of research outputs, and tracing influence on diplomatic negotiations and decision-making. Findings indicate structural and institutional differences produce distinct patterns of media and policy influence. US think tanks' influence lies not in 'knowledge production' but in three key elements: institutional independence, revolving-door networking with the diplomatic apparatus (the 'revolving door' phenomenon), and an aggressive media strategy. Iranian think tanks, despite scientific capacity and formal roles, pursue a largely indirect and more limited pattern of influence due to institutional and media constraints. Without presuming the inherent superiority of any one model, this research emphasizes the need to understand different institutional contexts and to rethink Iranian think tanks' communication strategies. It insists that without reforming institutional frameworks and creating intermediary channels (such as media) between think tanks and the diplomatic structure, expecting increased influence on diplomacy and public opinion would be unrealistic.