John’s University School of Law in New York City. He is a co-founder of the weblog Opinio Juris, www.opiniojuris.org. From 2004 -2006 he served on a legal assessment mission concerning the attempted secession of Transnistria from Moldova. An expanded version of this essay appeared as an American Society of International Law Insight, available at http://www.asil.org/insights/2008/02/insights080229.html .