This paper was written as a keynote address for a conference on Michael Walzer’s Just and Unjust War on the 40th anniversary of its publication. It discusses the significance of the book, and examines the updating prefaces Walzer wrote to the five editions of the book and his methodological postscript to the fifth edition. The paper contrasts Walzer’s philosophical method with that of analytic just war theory, arguing that Walzer’s use of historical cases and the analytic use of imaginary “toy” cases serve different philosophical ends. Noting that Just and Unjust Wars appeared the same year as the Additional Protocols to the Geneva Conventions, I examine the parallels between Walzer’s views and those in AP I, especially between Walzer’s ref...