Lawyers trained in U.S. law schools learn that the Constitution gives Congress the power "[t]o define and punish... offenses against the Law of Nations." Some might also be able to cite the oft-quoted dicta from the Supreme Court's decision in The Paquete Habana that "International law is part of our law, and must be ascertained and administered by the courts of justice of appropriate jurisdiction, as often as questions of right depending upon it are duly presented for their determination." But what does this mean for today's practitioner? One century after Paquete Habana, we ask what is international law, how does it affect U.S. legal practice, and how should the law schools prepare their students?

This article will proceed with the following main arguments:

1. What we call "international law" is currently in a period of rapid transformation;

2. It is more important than ever that graduating law students have at least a basic knowledge of the structure and instruments of public and private international law, as well as comparative law, because:

a. International law is increasingly part of the U.S. lawyer's world, whether they know it [or] not; and,

b. U.S. law has been and continues to be a defining feature of international law.

By assessing how the practice of law is evolving, this article hopes to provide signposts for ways in which the academy should adjust the methods and substance of legal education.