This document has also been published under the title ‘‘Joint letter from John Bellinger and William Haynes to Jakob Kellenberger on Customary International Law Study’’, in International Legal Materials, 46 ILM 514 (2007). Jean-Marie Henckaerts and Louise Doswald-Beck, Customary International Humanitarian Law, Cambridge University Press/ICRC, Cambridge 2005 (hereinafter, ‘‘Study’’). On November 11, 2006, the General Counsel of the Department of Defense and the Legal Adviser for the Department of State transmitted a letter to the President of the International Committee of the Red Cross, Dr. Jakob Kellenberger, providing the U.S. Government’s initial reactions to the Study. This article reflects the contents of that letter, which is available at, http://www.state.gov/s/l/rls/82630.htm. and, http://www.defenselink.mil/home/pdf/Customary_International_Humanitiarian_Law.pdf.