Christina Duffy Ponsa is a Professor of Law at Columbia University School of Law where her work focuses on American legal history. She is the co-editor ofForeign in a Domestic Sense: Puerto Rico, American Expansion, and the Constitution(Duke University Press, 2001), and the author of several articles and essays on the constitutional implications of American territorial expansion. She is currently at work on a constitutional and international legal history of American empire in the late nineteenth and early twentieth centuries. Professor Ponsa 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 Jose A. Cabranes on the Second Circuit Court of Appeals and to Justice Stephen G. Breyer on the United States Supreme Court.