This paperback, break-out edition, which focuses solely on foreign relations law, is derived from the popular and seminal casebook, Foreign Relations and National Security Law (4th ed. 2012). Full treatment is given to the nature and structure of the field, customary international law and treaties as sources of law in the United States, the power of the purse, federalism, and justiciability. Key issues concerning the war power are covered, but less than in the hardback edition. Issues relating to the investigation and prosecution of threats to national security, and the control of information relating to national security, are not addressed.