On 8 February 2007, at the Kellogg Conference Center at the Columbia University School of International and Public Affairs (SIPA), the Journal of International Affairs and the Middle East Institute hosted a live debate between Scott Sagan and Kenneth Waltz. The two political scientists revisited their classic debate on nuclear weapons, addressing recent developments in Iran and possible global responses. Richard K. Betts moderated the event. Dean Lisa Anderson delivered opening remarks. This article is a transcript of the discussion.