University of Chicago Law School Chicago Unbound Coase-Sandor Working Paper Series in Law and Coase-Sandor Institute for Law and Economics Economics 1998 A Theory of Customary International Law Eric A. Posner Jack L. Goldsmith Follow this and additional works at: https://chicagounbound.uchicago.edu/law_and_economics Part of the Law Commons Recommended Citation Eric Posner & Jack L. Goldsmith, "A Theory of Customary International Law" (John M. Olin Program in Law and Economics Working Paper No. 63, 1998). This Working Paper is brought to you for free and open access by the Coase-Sandor Institute for Law and Economics at Chicago Unbound. It has been accepted for inclusion in Coase-Sandor Working Paper Series in Law and Economics by an authorized administrator of Chicago Unbound. For more information, please contact
[email protected]. CHICAGO JOHN M. OLIN LAW & ECONOMICS WORKING PAPER NO. 63 (2D SERIES) A THEORY OF CUSTOMARY INTERNATIONAL LAW Jack L. Goldsmith and Eric A. Posner THE LAW SCHOOL THE UNIVERSITY OF CHICAGO This paper can be downloaded without charge at: The Chicago Working Paper Series Index: http://www.law.uchicago.edu/Lawecon/workingpapers.html The Social Science Research Network Electronic Paper Collection: http://papers.ssrn.com/paper.taf?abstract_id=145972 cil\draftnov4 A Theory of Customary International Law Jack L. Goldsmith1 & Eric A. Posner2 Customary international law (“CIL”) is one of two primary forms of international law, the other being the treaty. CIL is typically defined as a “customary practice of states followed from a sense of legal obligation.”3 Conventional wisdom views CIL as a unitary phenomenon that pervades international law and international relations.