Christina Duffy Ponsa is the George Welwood Murray Professor of Legal History at Columbia Law School, where she teaches constitutional law and American legal history. Professor Ponsa is the author of several articles on the constitutional law and history of American territorial expansion and empire, and co-editor of Foreign in a Domestic Sense: Puerto Rico, American Expansion, and the Constitution (Duke U. Press, 2001). She holds degrees from Princeton (A.B. 1990, Ph.D. 2010), Cambridge (M.Phil. 1995), and Yale (J.D. 1998). Before joining the Columbia faculty in 2007, she served as a law clerk to Judge José A. Cabranes on the Second Circuit Court of Appeals and to Justice Stephen G. Breyer on the United States Supreme Court.