This introductory essay elucidates the purpose and major themes of the special issue. The contributors to the issue provide an in-depth look at the Pugwash Conferences for Science and World Affairs (usually referred to as just Pugwash) to explore important themes in Cold War history. Among other topics covered in the issue are the impact of Pugwash in many countries, the nature of its organization, and the distinctive way in which it worked, as well as its importance for the relationship between scientists and the Cold War states and its role as a political actor and as a transnational actor. All of these issues and more make Pugwash a compelling subject for scholars of the Cold War.